Where did that come from?

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Update: Oct. 24, 2005

There are always lots of threads on the boards asking about the origins of various elements of Dungeons and Dragons. It's hard to say exactly where many of the creatures that make the game unique or have been borrowed so often as to become cliché come from. There are numerous sources to choose from, and they don't always agree about what a certain monster is. This thread is meant to be a reference point, and a path for the curious to begin their own research, not as the final word on exactly what caused the numerous writers and game designers who have made the various creatures (and various forms of the same creature for different editions) over the years. Those writers and designers would have to tell us that, and even they might not be sure what exactly inspired some of their creations. These are, in many instances, best guesses.

I've gone through the Monster Manual and noted where in myth, folklore, or literature certain creatures have come from. I'd ask for the community's assistance to correct any errors I've made, and to help me fill in the blanks. Please feel free to chime in with any information you might have.

Also, if anyone knows of the origin of an invented monster (which edition of D&D it originally came from, and which sourcebook/module and the author, if possible), I'll also incorporate that information as well.

Thanks to everyone that’s contributed their thoughts and opinions so far! Please keep up the feedback. Also, since Regdar's Repository is a slow board, feel free to PM me with information. There are still a few monsters that are unaccounted for, but many of the stragglers seem like they might have just been invented for the game.

So, without further ado, here is the list of creatures in the Monster Manual (minus animals and vermin) and their source, to the best of my knowledge or the knowledge of my fellow boards members, from mythology, folklore, literature, or pop culture.


Aboleth: Based on H.P. Lovecraft's Cthulhu stories according to Dragon Magazine
Achaierai: Possibly Greek mythology, but the creature lives on the Plane of Acheron, which is a name from Greek myth, so it may just sound Greek because it's named after its home.
Allip: A type of ghost, possibly Welsh
Angel: Judeo-Christian
Astral Deva: linguistically Hindu/Persian
Planetar, Solar: based on Dante's Paradiso?
Animated Object: various myths, legends and folklore, esp. Walt Disney's Fantasia and the German poltergeist legends
Ankeg: invented?
Aranea: Possible Tolkien influence (he liked spider monsters), or from the Greek myth of Arachne (although Arachne got transformed into a normal spider, not a spellcasting monstrous one). To my knowledge, it first appeared in Module X1, The Isle of Dread.
Archon: Zoroastrian/Gnostic myths, some types possibly invented.
Trumpet Archon: Seems to be based on the Angelic hosts that appeared to the shepherds to announce the birth of Christ in the New Testament.
Arrowhawk: the name seems inspired by the Stymphalian Birds, which Hercules took care of as his Fifth Labor, but the extra wings and lightning attack make me sceptical that the creature in the game is based on myth. The Stymphalian Birds just had razor sharp feathers.
Assassin Vine: Possibly based on certain predatory plants, only on a scale large enough to hunt humans.
Athach: It first appeared in the Mentzer Masters Set DM's Book as far as I know. The name corresponds to a Biblical land, but I don't know if there is a connection to the monster.
Azer: Justisaur suggests the Irish Dinnshenchas as inspiration, but what I've read of these Celtic dwarfs has nothing to do with fire.
Barghest: English folklore, more or less as presented in the game—a goblin wolf creature, related to the “Black Dog” legends—hell hounds, yelp hounds, the hounds of the Wild Hunt, etc.
Basilisk: Ancient/Medieval folklore
Behir: First appeared in the module The Lost Caverns of Tsojcath by Gygax
Beholder: An intellectual property of WotC (aka invented for the game), play on the proverb “beauty is in the eyes of the beholder.”
Created by Rob Kuntz.
Belker: invented?
Blink Dog: invented?
Bodak: English folklore (equivalent to Bugbear/Boogeyman in
folklore)
Bugbear: English folklore, a prank-playing fairy or the Boogeyman
Bulette: Based on old maritime tales, and a 70's era “dinosaur”
toy (see Rust Monster)
Carrion Crawler: An intellectual property of WotC (aka invented for the game) Celestial Creature (template): various mythologies
Centaur: Greek mythology
Chaos Beast: Cthulhu stories, apparently. Somewhat similar to John Carpenter's The Thing
Chimera: Greek mythology, see the Bellerophon legend
Choker: invented?
Chuul: Based on H.P. Lovecraft's Cthulhu stories according to Dragon Magazine
Cloaker: invented?
Cockatrice: Ancient/Medieval folklore
Couatl: Aztec folklore, based on the god Quetzlcouatl
Darkmantle: Based on the Piercer, a staple of older editions, most likely invented by TSR writers.
Delver: invented?
Demon: various mythologies/religions
Babau: Italian folklore?
Balor: Tolkien (Balrog), the name comes from Irish myth, where Balor was a Fomorian with a deadly eye that was usually closed.
Bebilith: Possibly based on Tolkien's
Dretch: invented?
Glabrezu: invented? The name seems to come from the word “glabrous”
which means “hairless”
Hezrou: invented?
Marilith: Possible inspiration from Hindu Naga or Greek Echidna
Nalfeshnee: invented?
Quasit: Invented to be the demonic equivalent of the imp
Retriever: invented
Succubus: Medieval folklore
Vrock: possibly inspired by the Etruscan vulture demon Charun
Derro: based on the writings of Richard Sharpe Shaver, who believed them to be the devolved offspring of aliens who remained on Earth when their parents left.
Destrachan: invented?
Devil: various mythologies/religions
Barbed Devil (Hamatula): Dante's Inferno
Bearded Devil (Barbazu): Dante's Inferno
Bone Devil (Osyluth): Dante's Inferno or medieval art seems the most likely inspiration.
Chain Devil (Kyton): invented?
Erinyes: In Greek mythology, Erinyes were actually The Fates, not another variation of the Succubi.
Hellcat (Bezekira): invented?
Horned Devil (Cornugon): Dante's Inferno
Ice Devil (Gelugon): Dante's Inferno
Imp: European folklore
Lemure: Roman mythology, a minor deity of the home, or a deceased spirit
Pit Fiend: Possibly derived from Dante's Inferno, although I can't find a direct match. It could be inspired by medieval art.
Devourer: invented?
Digester: invented?
Dinosaur: historical
Dire Animal: pseudo-historical, similar to real prehistoric animals in many respects. The Conan stories have many similar creatures in them.
Displacer Beast: invented?
Doppleganger: German folklore
Dragon: various mythologies, but the D&D Chromatic dragons most resemble European dragons such as Fafnir (from the Volsung/Niebelung legend), or the dragon slain by St. George in the early Christian legend, although most dragons only breathe fire or poison in legends, not acid, cold or lightning. The Gold Dragon seems to be inspired by the Chinese “Long” (“Lung” in Wade-Giles romanization and OA). The other metalics seem to have been invented to even out the lists of good and evil dragons.
Dragon Turtle: Chinese mythology has a draconic turtle creature, but the D&D version seems similar to a giant turtle in the Arabian Sindbad legends.
Dragonne: I'd guess invented by TSR, as the toy Dragonne (tm) I had as a kid was trademarked.
Drider: Most likely invented when the Drow became more developed.
Dryad: Greek mythology, although Chinese legends also contain many tree-spirits that seduce mortals and die if their tree is killed.
Dwarf: Scandinavian/Germanic mythology
Duergar: English folklore, possibly imported by the Normans from France/Spain.
Eagle, Giant: Tolkien
Eladrin: An intellectual property of WotC (aka invented for the
game)
Elemental: Based on Greek philosophy of elements, only come to life.
Elf: Scandinavian/Celtic mythologies
Drow: Scottish folklore, also spelled “Trow.” “Dark Elves” also appear in Scandinavian myths, but D&D's Drow culture and abilities were created for the game.
Ethereal Filcher: invented?
Ethereal Marauder: invented?
Ettercap: Tolkien, The Hobbit, who used an archaic term for spider (attercop), which is linguistically similar to a Saxon small poisonous snake-man, the Attorcroppe (Little Poison Head).
Ettin: English folktales, from Scandinavian mythology, English “ettin” (also etin) is a linguistic variation of Norse Jotun, or Giant. Every giant in Norse myth that I've ever read about only had one head, but two- and three-headed ogres and giants have popped up in numerous English folktales.
Fiendish Creature (template): various mythologies
Formian: Like many planar creatures, I'm guessing these guys were invented.
Frost Worm: From Robert E. Howard's Conan story Lair of the Ice Worm
Fungus: based on actual fungi and slime moulds
Gargoyle: Medieval architecture
Genie: Arabian folklore
Ghost: various mythologies, the dead coming back to haunt the living is fairly universal.
Ghoul: Arabian folklore, a demon of wastelands that robs graves for food when there are no living victims handy.
Giant: various mythologies, again stories of really big people are pretty universal
Cloud Giant: Jack and the Beanstalk
Fire Giant: Scandinavian mythology
Frost Giant: Scandinavian mythology
Hill Giant: various mythologies, your standard “giant”
Stone Giant: Stone Giants throwing boulders in a thunderstorm are mentioned in The Hobbit.
Storm Giant: Greek mythology? They seem like a blend of Zeus and Poseidon to me. Plus a bit of the Jolly Green Giant of canned vegetable fame.
Gibbering Mouther: Possibly inspired or taken from Cthulhu stories.
Girallon: Possibly based on a creature from Moorcock's Stormbringer series.
Githyanki: An intellectual property of WotC (aka invented for the game)
Githzerai: An intellectual property of WotC (aka invented for the game)
Gnoll: Come from a story (or stories) by Lord Dunsany, according to Justisaur. The Egyptian god Anubis (who had a jackal
head) could be another source.
Gnome: French folklore
Goblin: European folklore, in general any malicious fairy is a goblin.
Golem: The original in Jewish folklore is the Clay Golem.
Flesh Golem: Frankenstein
Iron Golem: Possibly based on the Greek myths of giant animated statues, such as Talos (See Harryhausen's Jason and the
Argonauts
) and King Minos of Crete's guardian.
Stone Golem: A variation on the Clay Golem?
Other Golems: Either inventions of TSR/WotC writers, or variations on animated statues of other sorts.
Gorgon: The name comes from Greek mythology (Medusa and her sisters were the Gorgons), but the bull form is possibly derived from the Ethiopian Catoblepas (which usually gets statted up as a separate monster), which according to Pliny was a bull-like monster with poisonous breath.
Gray Render: invented?
Grick: invented?
Griffon: Ancient folklore, related to the Sphinx, Mesopotamian Cherub, Lamassu, Manticore, and other “half-lion” creatures.
Grimlock: Probably inspired by the Morlocks in H.G. Wells'
The Time Machine
Guardinal: An intellectual property of WotC (aka invented for the game)
Hag: various mythologies, quite common in English and German folk and fairy tales Half-Celestial (template): various mythologies Half-Dragon (template): Apparently invented, I haven't come across any myths or legends of dragons spawning cross-breeds.
Half-Fiend (template): various mythologies
Halfling: Tolkien's Hobbits. Tolkien was most likely inspired by various fairy legends, and the term “hobbit” is linguisticly similar to “hob,” a prankster sprite.
Harpy: Greek mythology
Hell Hound: British folklore of the “Black Dog,” which influenced The Hound of the Baskervilles by Arthur Conan Doyle.
Related to Barghests, and the hounds of the Wild Hunt.
Hippogriff: Ancient/Medieval folklore
Hobgoblin: English folklore, another term for a goblin, although folklore hobgoblins are usually less malicious.
Homunculus: Ancient/Medieval folklore
Howler: invented?
Hydra: Greek mythology, see the Hercules legend.
Inevitable: Like many other planar denizens, I'm guessing this was invented.
Invisible Stalker: While invisible spirits and fairies are common in many myths and legends, this incarnation seems to be a TSR original.
Kobold: A fey living in mines, or in homes similar to a Brownie in German folklore, linguistically related to the word “goblin” in English
Kraken: Scandinavian folklore (I double checked, and early written accounts come from Norway), and most likely inspired by actual giant squid attacks on ships. The Kraken in Clash of the Titans was Harryhausen's poetic license.
Krenshar: invented?
Kuo-Toa: An intellectual property of WotC (aka invented for the game), based on H.P. Lovecraft's Cthulhu stories according to Dragon Magazine, but completely invented by Gygax according to the man himself (he doesn't say if Cthulhu was in inspiration for this invention or not).
Lamia: Greek mythology
Lammasu: Mesopotamian mythology, related to the Sphinx, Mesopotamian Cherub, Griffon, Manticore, and other “half-lion”
creatures.
Lich: The term is Old English for corpse. The undead spellcaster whose life force is tied to a secret object is possibly based on the Russian legend of "Kotshchey the Deathless" a nearly immortal magician.
Lillend: invented?
Lizardfolk: A staple of D&D since 1st Edition, there are numerous humanoid reptiles in world myths and legends, but it's hard to peg one as the original Lizard Man. Conan stories may be one source, and Spiderman comics are maybe a less likely, but possible inspiration.
Locathah: Possibly a variation of the mermaid, or maybe a creature from the Cthulhu stories. [The name seems similar to other Lovecraft names...] Lycanthrope : European and Asian folklore
Magmin: invented?
Manticore: Persian/Indian/SE Asian folklore, related to the Sphinx, Mesopotamian Cherub, Lamassu, Griffon, and other “half-lion”
creatures.
Medusa: Greek mythology, see the Perseus legend. Medusa was originally a proper name, and she and her sisters Stheno and Euryale were known as the Gorgons. A glance from them could kill or petrify.
Medusa was the only mortal of the sisters, and she was killed by Perseus.
Mephit: “Mephitis” means the stink of sulfer found around volcanoes and geysers, which is probably where the name comes from, and the form is just that of an imp. Giving them elemental qualities is, I'm assuming, an invention of the game writers.
Merfolk: Ancient/Medieval folklore, possibly first inspired by the Mesopotamian god Dagon, who was depicted as half man, half fish.
Mimic: invented?
Mind Flayer: An intellectual property of WotC, based on H.P.
Lovecraft's Cthulhu stories according to Dragon Magazine, but according to Gygax, he based them off of the cover art of Brian Lumley's novel The Burrowers Beneath, which is (apparently) a Cthulhu-inspired book.
Minotaur: Greek mythology, see the Theseus legend.
Mohrg: invented?
Mummy: Universal Studios movies from the 1930's contain the first instances of Egyptian mummies animating and killing people.
Numerous cultures mummify remains, but the idea of those mummies reanimating seems to have originally been a conceit of Hollywood.
Naga: Hindu mythology
Night Hag: English folklore
Nightmare: Possibly based on the mount of the Headless Horseman in The Legend of Sleepy Hollow, medieval Christian artwork, or the Piers Anthony Xanth novels. Or maybe just on the pun with bad dreams.
Nightshade : I believe these undead were invented by TSR writers. They first appeared, to my knowledge, in the Masters set by Mentzer.
Nymph: Greek mythology
Ogre: European folklore
Ogre Mage: East Asian folklore
Ooze: Based on actual corrosive molds and slimes, only on a bigger scale than normally found in nature. Movies like The Blob may have also influenced them.
Orc: Tolkien seems to have invented the humanoid form, based on stories of “goblins” or other malicious fey. Earlier references to a monster called an “Orc” seem to refer to killer whales (orcas), or to evil spirits in general.
Otyugh: invented?
Owl, Giant: Obviously based on real owls, possibly made giant to serve as a counterpart to Giant Eagles.
Owlbear: A “hybrid of two common animals” creature from English folklore, similar to the Florida Skunkbear or the Western U.S.
Jackalope.
Pegasus: Greek mythology, see the Bellerophon legend. Pegasus was said to have sprung from the neck or spilled blood of Medusa when she was killed by Perseus.
Phantom Fungus: invented?
Phase Spider: invented?
Phasm: invented?
Planetouched: invented?
Pseudodragon: invented?
Purple Worm: invented?
Rakshasa: Hindu mythology, although the “killed by a blessed crossbow bolt” comes from the TV show Kolchak: the Night Stalker
Rast: invented?
Ravid: invented?
Remorhaz: Invented by Gygax in Dragon #2
Roc: Arabian folklore, see the tales of Sindbad the Sailor Roper : Invented by Gygax in The Strategic Review Rust Monster: inspired by a '70s era “dinosaur” toy
Sahuagin: Based on H.P. Lovecraft's Cthulhu stories according to Dragon Magazine
Salamander: Ancient/Medieval folklore
Satyr: Greek mythology
Sea Cat: A monsterized version of sea lions, using a literal interpretation of the name to make the creature
Shadow: Possibly based on the Shades of the dead in Greek myth, and possibly also from Peter Pan when his shadow gets away from him. In some earlier versions of D&D, Shadows were not undead.
Shadow Mastiff: Quite possibly linked to the Hell Hound/Barghest/Yelp Hound/Black Dog legends of England.
Shambling Mound: invented?
Shield Guardian: invented?
Shocker Lizard: invented?
Skeleton: various, props to Jason and the Argonauts for making them cool.
Skum: Possibly based on Lovecraft's “Deep Ones”
Slaad: An intellectual property of WotC (aka invented for the
game)
Spectre: English folklore, another term for a ghost
Sphinx: Greek mythology, related to the Mesopotamian Cherub, Lamassu, Griffon, Manticore, and other “half-lion” creatures. The Egyptian monument was named the Sphinx by the Greeks when they saw the resemblance of the monument to the creature.
Spider Eater: invented?
Sprite: Medieval folklore
Grig: East Anglia (England), synonymous with Pixie
Nixie: German folklore, with a direct influence from Poul Anderson's novel Three Hearts and Three Lions
Pixie: Scottish folklore, likely a phonetic derivation from the Picts.
Stirge: invented?
Swarm: real life swarms
Tarrasque: A dragon in French folklore
Tendriculos: invented?
Thoqqua: invented?
Titan: Greek mythology, the Titans were the gods before, and parents of most of the Olympians (Zeus, Hera, Poseidon, Hades, etc.)
Tojanida: invented?
Treant: Tolkien's Ents, although walking trees may be from earlier English folklore
Triton: Greek mythology
Troglodyte: Term for primitive peoples/cavemen. The creature in D&D could have been inspired by a 60's era movie called Trog about a cave dwelling monster.
Troll: Scandinavian mythology, the gangly green regenerating form comes from the novel Three Hearts and Three Lions by Poul Anderson.
Umber Hulk: An intellectual property of WotC (aka invented for the game)
Unicorn: Medieval folklore
Vampire: Eastern European folklore, see in particular Dracula by Bram Stoker (as if you needed me to tell you that...). While vampiric creatures exist in many cultures' myths and legends, the D&D form seems to be heavily inspired by Stoker, who heavily researched the Eastern European vampire when writing Dracula, according to the Vlad Tepes historians Radu Florescu and Raymond T. McNally.
Vampire Spawn: Eastern European folklore, see Vampire (above) Vargouille : Based on legends of a type of vampire whose head would detatch and seek victims.
Wight: The term is Old English for “man,” and the creature is based off of Tolkien's Barrow Wights in The Fellowship of the Ring
Will-O-Wisp: English folklore
Winter Wolf: invented?
Worg: Tolkien, The Hobbit and The Lord of the Rings
Wraith: Another term for a ghost, or the apparition of a living person who is about to die seen by loved ones (entered English through Scottish in the 16th Century, but possibly has a Norwegian root according to Wikipedia). The D&D Wraith takes some inspiration from Tolkien's Ringwraiths (Nazgul).
Wyvern: Welsh folklore
Xill: Based on a creature in A.E. Van Vogt's Voyage of the Space Beagle
Xorn: invented?
Yeth Hound: Based on “yell” or “yelp” hounds of British folklore, in other words just another term for hell hounds or barghests.
Yrthak: invented?
Yuan-Ti: An intellectual property of WotC (aka invented for the
game)
Zombie: The D&D monster most closely resembles Caribbean (Arrowak and Creole) folklore and numerous horror movies (which originally borrowed from the Caribbean folklore), although tales of the walking dead exist the world over.
Compare the MM against the SRD. If it's in the MM and not the SRD, then it's likely that Wizards (or at least their legal department) has a strong belief that that creature was developed specifically for D&D (and they're probably right.)

Which gives: beholder, carrion crawler, eladrin, githyanki, githzerai, guardinal, kuo-toa, mind flayer, slaad, umber hulk, yuan-ti.

Heck, you could label those "product identity" instead of "invented?"
The fungus are actually reminiscent of real life slime moulds, only about 6 times faster and many times bigger.
Some additional Info:

Aboleth: Lovecraft
Azer: invented?
Possibly Irish Dinnshenchas as inspiration
Chaos Beast: Probably Lovecraft
Marilith: Possible inspiration from Hindu Naga or Greek Echidna
- Kali?
Quasit: invented?
Just another form of Imp.
Vrock: invented?
Might be inspiration from Charun, a vulture demon.
Gibbering Mouther: Lovecraft
Gnoll: invented?
Lord Dunsany
Goblin: European folklore
Golem: Jewish folklore
That would specifically be the Clay Golem. The other ones (stone & iron) I'm not so sure about.
Flesh Golem: Frankenstein
Lich: English folklore?
Possibly Egyptian Origin
Lizardfolk: invented?
Originally Lizardmen in 1e. Various Mythologies include some sort of reptile men - usually it's more closely snake (like Yuan-ti) than lizard though.
Locathah: invented?
Another 'fish people' probably either based around Mermaids or Lovecraft
Sahuagin: invented?
Yet another 'fish people'...
Zombie: Caribbean
Actually Zombies have been around since Greek mythology, the walking dead being in various mythologies. The specific version in D&D is closest to Caribbean though.
Update: Feb 26th, 2006

There are always lots of threads on the boards asking about the origins of various elements of Dungeons and Dragons. It’s hard to say exactly where many of the creatures that make the game unique or have been borrowed so often as to become cliché come from. There are numerous sources to choose from, and they don’t always agree about what a certain monster is. This thread is meant to be a reference point, and a path for the curious to begin their own research, not as the final word on exactly what caused the numerous writers and game designers who have made the various creatures (and various forms of the same creature for different editions) over the years. Those writers and designers would have to tell us that, and even they might not be sure what exactly inspired some of their creations. These are, in many instances, best guesses.

I've gone through the Monster Manual and noted where in myth, folklore, or literature certain creatures have come from. I'd ask for the community's assistance to correct any errors I've made, and to help me fill in the blanks. Quite a few creatures on the list are ones that were made up by the game designers, but there may be some that I assume are made up that were actually from some myth or folktale, or a fantasy or sci-fi novel that I haven't read. So please feel free to chime in with any information you might have.

Also, if anyone knows of the origin of an invented monster (which edition of D&D it originally came from, and which sourcebook/module and the author, if possible), I'll also incorporate that information as well.

Thanks to everyone that’s contributed their thoughts and opinions so far! Please keep up the feedback. Also, since Regdar’s Repository is a slow board, feel free to PM me with information. There are still a few monsters that are unaccounted for, but many of the stragglers seem like they might have just been invented for the game.

So, without further ado, here is the list of creatures in the Monster Manual (minus animals and vermin) and their source, to the best of my knowledge or the knowledge of my fellow boards members, from mythology, folklore, literature, or pop culture.


Aboleth: Based on H.P. Lovecraft's Cthulhu stories according to Dragon Magazine. First appeared in Module I1 Dwellers of the Forbidden City.
Achaierai: Possibly Greek mythology, but the creature lives on the Plane of Acheron, which is a name from Greek myth, so it may just sound Greek because it's named after its home.
Allip: A type of ghost, possibly Welsh
Angel: Judeo-Christian
Astral Deva: linguistically Hindu/Persian
Planetar, Solar: based on Dante's Paradiso?
Animated Object: various myths, legends and folklore, esp. Walt Disney's Fantasia and the German poltergeist legends
Ankeg: invented?
Aranea: Possible Tolkien influence (he liked spider monsters), or from the Greek myth of Arachne (although Arachne got transformed into a normal spider, not a spellcasting monstrous one). To my knowledge, it first appeared in Module X1, The Isle of Dread.
Archon: Zoroastrian/Gnostic myths, some types possibly invented.
Trumpet Archon: Seems to be based on the Angelic hosts that appeared to the shepherds to announce the birth of Christ in the New Testament.
Arrowhawk: the name seems inspired by the Stymphalian Birds, which Hercules took care of as his Fifth Labor, but the extra wings and lightning attack make me sceptical that the creature in the game is based on myth. The Stymphalian Birds just had razor sharp feathers.
Assassin Vine: Possibly based on certain predatory plants, only on a scale large enough to hunt humans.
Athach: It first appeared in the Mentzer Masters Set DM's Book as far as I know. The name corresponds to a Biblical land, but I don't know if there is a connection to the monster.
Azer: Justisaur suggests the Irish Dinnshenchas as inspiration, but what I've read of these Celtic dwarfs has nothing to do with fire.
Barghest: English folklore, more or less as presented in the game—a goblin wolf creature, related to the “Black Dog” legends—hell hounds, yelp hounds, the hounds of the Wild Hunt, etc.
Basilisk: Ancient/Medieval folklore
Behir: First appeared in the module S4 The Lost Caverns of Tsojcath by Gary Gygax
Beholder: An intellectual property of WotC (aka invented for the game), play on the proverb “beauty is in the eyes of the beholder.” Created by Rob Kuntz.
Belker: invented?
Blink Dog: invented?
Bodak: English folklore (equivalent to Bugbear/Boogeyman in folklore). First appeared in Module S4 Lost Caverns of Tsojcanth.
Bugbear: English folklore, a prank-playing fairy or the Boogeyman
Bulette: Based on old maritime tales, and a 70's era “dinosaur” toy (see Rust Monster)
Carrion Crawler: An intellectual property of WotC (aka invented for the game)
Celestial Creature (template): various mythologies
Centaur: Greek mythology
Chaos Beast: Cthulhu stories, apparently. Somewhat similar to John Carpenter's The Thing
Chimera: Greek mythology, see the Bellerophon legend
Choker: invented?
Chuul: Based on H.P. Lovecraft's Cthulhu stories according to Dragon Magazine
Cloaker: invented?
Cockatrice: Ancient/Medieval folklore
Couatl: Aztec folklore, based on the god Quetzlcouatl
Darkmantle: Based on the Piercer, a staple of older editions, most likely invented by TSR writers.
Delver: invented?
Demon: various mythologies/religions
Babau: Italian folklore?
Balor: Tolkien (Balrog), the name comes from Irish myth, where Balor was a Fomorian with a deadly eye that was usually closed.
Bebilith: Possibly based on Tolkien's
Dretch: invented?
Glabrezu: invented? The name seems to come from the word “glabrous” which means “hairless”
Hezrou: invented?
Marilith: Possible inspiration from Hindu Naga or Greek Echidna
Nalfeshnee: invented?
Quasit: Invented to be the demonic equivalent of the imp
Retriever: invented
Succubus: Medieval folklore
Vrock: possibly inspired by the Etruscan vulture demon Charun
Derro: based on the writings of Richard Sharpe Shaver, who believed them to be the devolved offspring of aliens who remained on Earth when their parents left. First appeared in Module S4 Lost Caverns of Tsojcanth.
Destrachan: invented?
Devil: various mythologies/religions
Barbed Devil (Hamatula): Dante's Inferno
Bearded Devil (Barbazu): Dante's Inferno
Bone Devil (Osyluth): Dante's Inferno or medieval art seems the most likely inspiration.
Chain Devil (Kyton): invented?
Erinyes: In Greek mythology, Erinyes were actually The Fates, not another variation of the Succubi.
Hellcat (Bezekira): invented?
Horned Devil (Cornugon): Dante's Inferno
Ice Devil (Gelugon): Dante's Inferno
Imp: European folklore
Lemure: Roman mythology, a minor deity of the home, or a deceased spirit
Pit Fiend: Possibly derived from Dante's Inferno, although I can't find a direct match. It could be inspired by medieval art.
Devourer: invented?
Digester: invented?
Dinosaur: historical
Dire Animal: pseudo-historical, similar to real prehistoric animals in many respects. The Conan stories have many similar creatures in them.
Displacer Beast: invented?
Doppleganger: German folklore
Dragon: various mythologies, but the D&D Chromatic dragons most resemble European dragons such as Fafnir (from the Volsung/Niebelung legend), or the dragon slain by St. George in the early Christian legend, although most dragons only breathe fire or poison in legends, not acid, cold or lightning. The Gold Dragon seems to be inspired by the Chinese “Long” (“Lung” in Wade-Giles romanization and OA). The other metalics seem to have been invented to even out the lists of good and evil dragons.
Dragon Turtle: Chinese mythology has a draconic turtle creature, but the D&D version seems similar to a giant turtle in the Arabian Sindbad legends.
Dragonne: I'd guess invented by TSR, as the toy Dragonne (tm) I had as a kid was trademarked.
Drider: Most likely invented when the Drow became more developed.
Dryad: Greek mythology, although Chinese legends also contain many tree-spirits that seduce mortals and die if their tree is killed.
Dwarf: Scandinavian/Germanic mythology
Duergar: English folklore, possibly imported by the Normans from France/Spain.
Eagle, Giant: Tolkien
Eladrin: An intellectual property of WotC (aka invented for the game)
Elemental: Based on Greek philosophy of elements, only come to life.
Elf: Scandinavian/Celtic mythologies
Drow: Scottish folklore, also spelled “Trow.” “Dark Elves” also appear in Scandinavian myths, but D&D's Drow culture and abilities were created for the game.
Ethereal Filcher: invented?
Ethereal Marauder: invented?
Ettercap: Tolkien, The Hobbit, who used an archaic term for spider (attercop), which is linguistically similar to a Saxon small poisonous snake-man, the Attorcroppe (Little Poison Head).
Ettin: English folktales, from Scandinavian mythology, English “ettin” (also etin) is a linguistic variation of Norse Jotun, or Giant. Every giant in Norse myth that I've ever read about only had one head, but two- and three-headed ogres and giants have popped up in numerous English folktales.
Fiendish Creature (template): various mythologies
Formian: Like many planar creatures, I'm guessing these guys were invented.
Frost Worm: From Robert E. Howard's Conan story Lair of the Ice Worm
Fungus: based on actual fungi and slime moulds
Gargoyle: Medieval architecture
Genie: In Arabian folklore, creatures that were above humans but less than angels. The Dao and Marid first appeared in Module S4 Lost Caverns of Tsojcanth.
Ghost: various mythologies, the dead coming back to haunt the living is fairly universal.
Ghoul: Arabian folklore, a demon of wastelands that robs graves for food when there are no living victims handy.
Giant: various mythologies, again stories of really big people are pretty universal
Cloud Giant: Jack and the Beanstalk
Fire Giant: Scandinavian mythology
Frost Giant: Scandinavian mythology
Hill Giant: various mythologies, your standard “giant”
Stone Giant: Stone Giants throwing boulders in a thunderstorm are mentioned in The Hobbit, but only once. Tolkien scholars are divided on whether they are true giants, trolls, or even Ents (Sam Gamgee and Ted Sandyman have an argument about the existence (or not) of “these Tree-men, these giants, you might call them” in The Fellowship of the Ring.
Storm Giant: Greek mythology? They seem like a blend of Zeus and Poseidon to me. Plus a bit of the Jolly Green Giant of canned vegetable fame.
Gibbering Mouther: Possibly inspired or taken from Cthulhu stories.
Girallon: Possibly based on a creature from Moorcock's Stormbringer series.
Githyanki: An intellectual property of WotC (aka invented for the game)
Githzerai: An intellectual property of WotC (aka invented for the game)
Gnoll: Come from a story (or stories) by Lord Dunsany, according to Justisaur. The Egyptian god Anubis (who had a jackal head) could be another source.
Gnome: French folklore
Goblin: European folklore, in general any malicious fairy is a goblin.
Golem: The original in Jewish folklore is the Clay Golem.
Flesh Golem: Frankenstein
Iron Golem: Possibly based on the Greek myths of giant animated statues, such as Talos (See Harryhausen's Jason and the Argonauts) and King Minos of Crete's guardian.
Stone Golem: A variation on the Clay Golem?
Other Golems: Either inventions of TSR/WotC writers, or variations on animated statues of other sorts.
Gorgon: The name comes from Greek mythology (Medusa and her sisters were the Gorgons), but the bull form is possibly derived from the Ethiopian Catoblepas (which usually gets statted up as a separate monster), which according to Pliny was a bull-like monster with poisonous breath.
Gray Render: invented?
Grick: invented?
Griffon: Ancient folklore, related to the Sphinx, Mesopotamian Cherub, Lamassu, Manticore, and other “half-lion” creatures.
Grimlock: Probably inspired by the Morlocks in H.G. Wells' The Time Machine
Guardinal: An intellectual property of WotC (aka invented for the game)
Hag: various mythologies, quite common in English and German folk and fairy tales
Half-Celestial (template): various mythologies
Half-Dragon (template): Apparently invented, I haven't come across any myths or legends of dragons spawning cross-breeds.
Half-Fiend (template): various mythologies
Halfling: Tolkien's Hobbits. Tolkien was most likely inspired by various fairy legends, and the term “hobbit” is linguisticly similar to “hob,” a prankster sprite.
Harpy: Greek mythology
Hell Hound: British folklore of the “Black Dog,” which influenced The Hound of the Baskervilles by Arthur Conan Doyle. Related to Barghests, and the hounds of the Wild Hunt.
Hippogriff: Ancient/Medieval folklore
Hobgoblin: English folklore, another term for a goblin, although folklore hobgoblins are usually less malicious.
Homunculus: Ancient/Medieval folklore
Howler: invented?
Hydra: Greek mythology, see the Hercules legend.
Inevitable: Like many other planar denizens, I'm guessing this was invented.
Invisible Stalker: While invisible spirits and fairies are common in many myths and legends, this incarnation seems to be a TSR original.
Kobold: A fey living in mines, or in homes similar to a Brownie in German folklore, linguistically related to the word “goblin” in English
Kraken: Scandinavian folklore (I double checked, and early written accounts come from Norway), and most likely inspired by actual giant squid attacks on ships. The Kraken in Clash of the Titans was Harryhausen's poetic license.
Krenshar: invented?
Kuo-Toa: An intellectual property of WotC (aka invented for the game), based on H.P. Lovecraft's Cthulhu stories according to Dragon Magazine, but completely invented by Gygax according to the man himself (he doesn't say if Cthulhu was in inspiration for this invention or not).
Lamia: Greek mythology
Lammasu: Mesopotamian mythology, related to the Sphinx, Mesopotamian Cherub, Griffon, Manticore, and other “half-lion” creatures.
Lich: The term is Old English for corpse. The undead spellcaster whose life force is tied to a secret object is possibly based on the Russian legend of "Kotshchey the Deathless" a nearly immortal magician.
Lillend: invented?
Lizardfolk: A staple of D&D since 1st Edition, there are numerous humanoid reptiles in world myths and legends, but it's hard to peg one as the original Lizard Man. Conan stories may be one source, and Spiderman comics are maybe a less likely, but possible inspiration.
Locathah: Possibly a variation of the mermaid, or maybe a creature from the Cthulhu stories. [The name seems similar to other Lovecraft names...]
Lycanthrope : European and Asian folklore
Magmin: invented?
Manticore: Persian/Indian/SE Asian folklore, related to the Sphinx, Mesopotamian Cherub, Lamassu, Griffon, and other “half-lion” creatures.
Medusa: Greek mythology, see the Perseus legend. Medusa was originally a proper name, and she and her sisters Stheno and Euryale were known as the Gorgons. A glance from them could kill or petrify. Medusa was the only mortal of the sisters, and she was killed by Perseus.
Mephit: “Mephitis” means the stink of sulfer found around volcanoes and geysers, which is probably where the name comes from, and the form is just that of an imp. Giving them elemental qualities is, I'm assuming, an invention of the game writers.
Merfolk: Ancient/Medieval folklore, possibly first inspired by the Mesopotamian god Dagon, who was depicted as half man, half fish.
Mimic: invented?
Mind Flayer: An intellectual property of WotC, based on H.P. Lovecraft's Cthulhu stories according to Dragon Magazine, but according to Gygax, he based them off of the cover art of Brian Lumley's novel The Burrowers Beneath, which is (apparently) a Cthulhu-inspired book.
Minotaur: Greek mythology, see the Theseus legend.
Mohrg: invented?
Mummy: Bram Stoker's novel The Jewel of Seven Stars appears to be the first instance of a reanimated mummy stalking victims. Universal Studios movies from the 1930's made the idea of Egyptian mummies animating and killing people popular. Numerous cultures mummify remains, but their myths do not include them returning as Undead. Interesting to note, however, the Egyptian god Osiris was killed by Set then brought back to life by the other gods and was depicted as still wrapped in him mummification shrouds.
Naga: Hindu mythology
Night Hag: English folklore
Nightmare: Possibly based on the mount of the Headless Horseman in The Legend of Sleepy Hollow, medieval Christian artwork, or the Piers Anthony Xanth novels. Or maybe just on the pun with bad dreams.
Nightshade : I believe these undead were invented by TSR writers. They first appeared, to my knowledge, in the Masters set by Mentzer.
Nymph: Greek mythology
Ogre: European folklore
Ogre Mage: East Asian folklore. Many Japanese legends of Oni, and Chinese legends of demons/monsters, particularly Journey to the West involve these creatures.
Ooze: Based on actual corrosive molds and slimes, only on a bigger scale than normally found in nature. Movies like The Blob may have also influenced them.
Orc: Tolkien seems to have invented the humanoid form, based on stories of “goblins” or other malicious fey. Earlier references to a monster called an “Orc” seem to refer to killer whales (orcas), or to evil spirits in general. According to Bergan Evans' Dictionary of Mythology, Du Bartas (1589) mentions an “orque” and Holland (1650) mentions a “three headed orke,” both seem to be variant spellings of “ogre.”
Otyugh: invented?
Owl, Giant: Obviously based on real owls, possibly made giant to serve as a counterpart to Giant Eagles.
Owlbear: A “hybrid of two common animals” creature from English folklore, similar to the Florida Skunkbear or the Western U.S. Jackalope.
Pegasus: Greek mythology, see the Bellerophon legend. Pegasus was said to have sprung from the neck or spilled blood of Medusa when she was killed by Perseus.
Phantom Fungus: invented?
Phase Spider: invented?
Phasm: invented?
Planetouched: invented?
Pseudodragon: invented?
Purple Worm: invented?
Rakshasa: Hindu mythology, although the “killed by a blessed crossbow bolt” comes from the TV show Kolchak: the Night Stalker
Rast: invented?
Ravid: invented?
Remorhaz: Invented by Gygax in Dragon #2
Roc: Arabian folklore, see the tales of Sindbad the Sailor
Roper : Invented by Gygax in The Strategic Review
Rust Monster: inspired by a '70s era “dinosaur” toy
Sahuagin: Based on H.P. Lovecraft's Cthulhu stories according to Dragon Magazine
Salamander: Ancient/Medieval folklore
Satyr: Greek mythology
Sea Cat: A monsterized version of sea lions, using a literal interpretation of the name to make the creature
Shadow: Possibly based on the Shades of the dead in Greek myth, and possibly also from Peter Pan when his shadow gets away from him. In some earlier versions of D&D, Shadows were not undead.
Shadow Mastiff: Quite possibly linked to the Hell Hound/Barghest/Yelp Hound/Black Dog legends of England.
Shambling Mound: invented?
Shield Guardian: invented?
Shocker Lizard: invented?
Skeleton: various, props to Jason and the Argonauts for making them cool.
Skum: Possibly based on Lovecraft's “Deep Ones”
Slaad: An intellectual property of WotC (aka invented for the game)
Spectre: English folklore, another term for a ghost
Sphinx: Greek mythology, related to the Mesopotamian Cherub, Lamassu, Griffon, Manticore, and other “half-lion” creatures. The Egyptian monument was named the Sphinx by the Greeks when they saw the resemblance of the monument to the creature.
Spider Eater: invented?
Sprite: Medieval folklore
Grig: East Anglia (England), synonymous with Pixie
Nixie: German folklore, with a direct influence from Poul Anderson's novel Three Hearts and Three Lions
Pixie: Scottish folklore, likely a phonetic derivation from the Picts.
Stirge: invented?
Swarm: real life swarms
Tarrasque: A dragon in French folklore
Tendriculos: invented?
Thoqqua: invented?
Titan: Greek mythology, the Titans were the gods before, and parents of most of the Olympians (Zeus, Hera, Poseidon, Hades, etc.)
Tojanida: invented?
Treant: Tolkien's Ents, although walking trees may be from earlier English folklore
Triton: Greek mythology, originally a single sea god (son of Poseidon and Amphitrite), later applied to a host of lesser sea spirits with humanoid upper bodies and the lower bodies of fish.
Troglodyte: Term for primitive peoples/cavemen. The creature in D&D could have been inspired by a 60's era movie called Trog about a cave dwelling monster.
Troll: Scandinavian mythology, the gangly green regenerating form comes from the novel Three Hearts and Three Lions by Poul Anderson.
Umber Hulk: An intellectual property of WotC (aka invented for the game)
Unicorn: Medieval folklore
Vampire: Eastern European folklore, see in particular Dracula by Bram Stoker (as if you needed me to tell you that...). While vampiric creatures exist in many cultures' myths and legends, the D&D form seems to be heavily inspired by Stoker, who heavily researched the Eastern European vampire when writing Dracula, according to the Vlad Tepes historians Radu Florescu and Raymond T. McNally.
Vampire Spawn: Eastern European folklore, see Vampire (above)
Vargouille : Based on legends of a type of vampire whose head would detatch and seek victims.
Wight: The term is Old English for “man,” and the creature is based off of Tolkien's Barrow Wights in The Fellowship of the Ring
Will-O-Wisp: English folklore
Winter Wolf: invented?
Worg: Tolkien, The Hobbit and The Lord of the Rings
Wraith: Another term for a ghost, or the apparition of a living person who is about to die seen by loved ones (entered English through Scottish in the 16th Century, but possibly has a Norwegian root according to Wikipedia). The D&D Wraith takes some inspiration from Tolkien's Ringwraiths (Nazgul).
Wyvern: Welsh folklore
Xill: Based on a creature in A.E. Van Vogt's Voyage of the Space Beagle
Xorn: invented?
Yeth Hound: Based on “yell” or “yelp” hounds of British folklore, in other words just another term for hell hounds or barghests.
Yrthak: invented?
Yuan-Ti: An intellectual property of WotC (aka invented for the game). First appeared in Module I1 Dwellers of the Forbidden City.
Zombie: The D&D monster most closely resembles Caribbean (Arrowak and Creole) folklore and numerous horror movies (which originally borrowed from the Caribbean folklore), although tales of the walking dead exist the world over.

Monster Manual II

Abiel : Obviously based on real bees.
Asperi : The name is Latin for “rough, harsh, severe” but I can't seem to find any mythical or fictional creatures that match.
Automaton : The name is from Greek, meaning a self-acting or self-moving object. Clockwork automatons have been around since Ancient Egypt, but the first humanoid automaton design is credited to Leonardo Da Vinci according to Wikipedia.
Banshee : A spirit from Irish folklore, their wailing was said to be an omen of an impending death in the family.
Boggle : Cornish/Welsh name for a bog fairy. The Irish name, Ballybog, and the description of mud-covered, ugly, mischievious but not especially dangerous fairies reminds me a bit of the classic D&D Bullywug, but any connection is speculation on my part.
Bogun : In folklore terms, just another name for a goblin.
Bone Naga : As with the Nagas in the MM, the original is from Indian mythology.
Bronze Serpent : Possibly based on remnants of an early middle-eastern snake god, Nechushtan, whose bronze image was melted by the Hebrew king Hezekiah.
Catoblepas : As mentioned in the entry for the MM Gorgon, the Catoblepas was described by Pliny as a creature with a huge head that ate poisonous plants and thus had poisonous breath, and later called a Gorgon in a later beastiary.
Chaos Roc : The Roc is a creature from Arabian folklore (see the Sindbad stories), but the Chaos Roc seems to have been invented for the game.
Cloaked Ape : Based on real world flying squirrels, similar to an unevolved version of the Phanaton found in the module X1 Isle of Dread.
Clockwork Horror : see Automaton, above.
Corpse Gatherer : Probably just invented, but it reminds me a lot of the boss creature Legion in Castlevania: Symphony of the Night, which is a creature that covers itself in a ball of corpses.
Crimson Death : Could be based on Edgar Allen Poe's The Masque of the Red Death, in which a spectral embodiment of a disease kills a group of aristocrats who sought to escape the pestilence by locking themselves in a castle.
Darktentacles : Based on Tolkien's guardian of the gates of Moria in The Lord of the Rings.
Devil, Malebranche : Based on Dante's Inferno.
Dinosaus (all) : As with the MM dinosaurs, based on prehistoric dinosaurs.
Dire Animal (all) : As with the MM dire animals, extrapolated from prehistoric creatures.
Dread Guard : The animated suit of armor is a staple of the fantasy genre, especially in video games.
Effigy : An effigy is a representative of a person or ideal. In rituals, effigies of evil spirits are burned as a form of exorcism/warding. The flaming undead was most likely inspired by this practice.
Firbolg : A race of giants from Irish mythology, who battled the Fomorians and Tuatha de Danaan.
Fomorian : A race of giants from Irish mythology, who battled the Firbolg and Tuatha de Danaan. First appeared in Module S4 Lost Caverns of Tsojcanth.
Forest Sloth : Based on the Megatherium, a prehistoric giant sloth.
Gambol : Possibly based on Robert E. Howard's Conan stories, which feature many large ape-like creatures.
Giant : While giants are native to most cultures' myths and folktales, these all seem to be invented for the game.
Golem : As mentioned in the MM listing for Golems, the original golem comes from Jewish folklore. Most types of golems in D&D were invented for the game.
Stained Glass Golem: The movie Young Sherlock Holmes features an animated stained glass warrior, but I'm not sure if that preceeds the first instance of the creature in D&D or not.
Greenvise : This seems to be inspired by Audrey II in Little Shop of Horrors.
Grimalkin : In MacBeth, the witches' cat was named Grimalkin.
Grizzly Mastodon : A monstrous version of the wooly mammoth.
Juggernaut : The term comes from Sanskrit “jagannath,” meaning “Lord of the Universe” (a reference to Krishna), and came into English meaning an unstoppable crushing force because of Hindu festivals featuring huge chariots that sometimes crushed festival attendees.
Legendary Animals : A staple of fantasy and childrens literature are extraordinary versions of normal animals. A prime example would be the legendary horse Shadowfax in Lord of the Rings.
Leviathan : A biblical sea serpent of immense size, based on a Canaanite god, and later during the middle ages equated with a devil that will be destroyed in the End Times.
Megalodon : A prehistoric shark.
Megapede : A monstrous version of real centipedes.
Phoenix : A magical firebird from Egyptian mythology, at the end of its life, it built a nest, immolated itself, and its offspring would rise from the ashes. The Chinese feng-huang is often translated into English as “phoenix” but other than being a magical bird, and in Taoist geomancy is the guardian spirit connected with the element Fire, the Chinese version bears little resemblance to the Egyptian-based phoenix.
Shadow Spider : Bears a resemblance to Ungoliant from Tolkien's Silmarillion, but it's not an exact match.
Sirine : Greek nymphs (also spelled siren or seirene) who lured sailors with their beautiful singing voices, sometimes depicted as human women, other times as half-human half-bird, or as mermaids. The woman-bird siren apparently gave the D&D harpy its luring song, as the Greek mythical harpy was just a hideous bird-woman.
Sylph : An air spirit from medieval alchemical folklore.
Yugoloth: Marraenoloth : Based on the Greek Charon, who ferried souls across the river Acheron into Hades.
Razorboar : Based on the Twrch Trwyth and her offspring in Welsh mythology (see Culhwch and Olwen in the Mabinogion.
Wikipedia has a good article on this very issue, If I remember correctly...

Also, one could search a lot of the cryptozoological sites available online.
http://www.pantheon.org/mythica.html
Might help for further information.

-I'm fairly certain the Aboleth comes from sea culture myths- maybe derived from something else.
The wight is based on Tolkein's barrow wight: this is even explicitly stated in older D&D editions.
the derro are from the writings of Richard Sharpe Shaver. http://en.wikipedia.org/wiki/Richard_Sharpe_Shaver (this article blew my mind)
The Derro are based on a similar race (Dero) included as part of phenomena known as "The Shaver Mystery." Its creator, a since fiction writer named Richard Sharpe Shaver, wrote of an ancient, scientifically advanced community of beings who lived inside the Earth. When theses creatures abandoned our planet, they left their most disabled offspring behind. It was this insane population that was referred to as the Dero.

These stories were debated as truth by many conspiracy buffs during the 1940's. There were countless sightings of these creatures reported. One such report was an from an American serving in Burma during WWII. He claimed that a Dero had wounded him with some sort of energy weapon.
Arrowhawk: invented?
Assassin Vine: invented?
Girallon: invented?
Hell Hound: The Hound of the Baskervilles?
Troglodyte: invented? Term for primitive peoples/cavemen

These few entries I am absolutely certain on. Others I have left off, as I was unsure. The arrowhawk, assassin vine, girrallon, hell hound, and troglodyte are all taken from classic mythology, though I couldn't say specifically which cultures. I believe, however, that the assassin vine and arrowhawk are Greek.
The Gorgon of Greek Myth was a bull. The Medusa poured out of the dead Gorgons neck.

No. The gorgon were what D&D calls the medusas. The Medusa was the only mortal one of them.

Kraken is Greek, watch the Clash of the Titans "Release the Kraken!!!"

Norse or medieval, if written sources are to be believed.

Merfolk were from Greek first, children of Poseidon.

As much as the Kraken. Probably quite common everywhere among sailors, I'd say.
Zombie: Caribbean folklore

And in turn, I *think* from African folklore (brought over via the slave trade)

Ghoul: English folklore

I think that one's actually Hindu/Indian. Or at least I've seen a fair number of references to a corpse-eating Ghul.

Ooze: invented?

Similar things were certainly present in general fantasy lore before D&D. Compare Lovecraft's Shoggoth or other stories from Weird Tales (a serial in which Lovecraft published).

Gnoll: invented?
Lord Dunsany

Really? Which story?
No. The gorgon were what D&D calls the medusas. The Medusa was the only mortal one of them.

Correct. The "gorgon as iron-plated bull" has an interesting history, in fact.

The creature is actually called a catoblepas (yeah, I know, that's another monster entirely in D&D), first reported by Pliny the Elder, a great Greek collector of folklore. Pliny claimed to have seen most of it first-hand, the liar.

The catoblepas, Pliny reported, lives in Ethiopia and looks like a bull with steel scales and a huge, heavy head. Its name means "looking down", because that's what it did; it looked down most of the time because of the skull's weight. This was fortunate, apparently, because it could kill with a look.

Later, Claudius Aelianus got a hold of it and changed the story a little; now it wasn't death with a look, but toxic breath -- the creature breathed poisonous gas that killed everything nearby, because it ate poisonous plants. (For the record, both of them probably had seen a gnu, which does look like a bull with a huge, heavy head, and which is known for eating plants that no other animal will touch.)

In France, many centuries later, Gustave Flaubert mentioned the catoblepas in a book of his. Apparently he referred to it as a Gorgon as well, as an allusion to the more commonly-known death-gaze legend.

That seems to be where D&D picked it up and made a steel bull called Gorgon, instead of Catoblepas, which would be more correct and less confusing.


GHOUL
The Ghoul (or ghul) comes from Musilm folklore. It's a beast that feeds on the bodies of the dead in tombs or on little children, and can take the form of an animal. It's half-and-half child-scaring boogieman and a personification of the terror of empty desert wastes.

BULETTE
While the Candygram was funny, stories of a land-shark are as old as sailing.
Golems: The clay golem is Jewish. The metal golems may be based on the rock-throwing 'robot' created by Daedulus for the King of Crete in Greek mythology (the same guy that had the minotaur). While there may be specific instances of other golems, my assumption is that the D&D designers basically took the idea and ran with it to create a variety of creatures.

Can anyone tell me the French story of the Tarrasque? I'm curious as to what folk tale could create this horrible walking maw.
IIRC, Lemures were spirits of the dead in Roman mythology (in the Greek, they were Manes).
Here's the first revision of the list. Thanks to everyone that's helped point me in the right direction so far! Keep that information coming!

Also, I'm looking for information on when the creatures first appeared in D&D. I started out with the Mentzer BECM box sets, and never had a 1E AD&D Monster Manual of my own, or an earlier set of the original D&D, or many modules, so any help in this area would be appreciated.

P.S. WizO_Sith, or whoever is in charge of evaluating these posts, is it possible to edit the first post in the thread with this updated information? There's obviously no edit function here in Regdar's Repository.

[Regdar replies: Feel free to send in an edited version to boards@wizards.com to replace a posted version. Alternately, start a new thread and post a reply to the old thread linking to the new.)
____________________________________________________
Aboleth: possibly based on Cthulhu stories, or possibly maritime folklore
Achaierai: invented?
Allip: invented?
Angel: Judeo-Christian
Astral Deva: linguistically Hindu
Planetar, Solar: based on Dante's Paradiso?
Animated Object: various, esp. Walt Disney
Ankeg: invented?
Aranea: invented? Possible Tolkein influence. To my knowledge, it first appeared in Module X1, The Isle of Dread.
Archon: Judeo-Christian, some types possibly invented
Arrowhawk: the name seems inspired by the Stymphalian Birds, which Hercules took care of as his Fifth Labor, but the extra wings and lightning attack make me sceptical that the creature in the game is based on myth.
Assassin Vine: Possibly based on certain predatory plants, only on a scale large enough to hunt humans.
Athach: It first appeared in the Mentzer Masters Set DM's Book. The name corresponds to a Biblical land, but I don't know if there is a connection to the monster.
Azer: Justisaur suggests the Irish Dinnshenchas as inspiration, but what I've read of these Celtic dwarfs has nothing to do with fire.
Barghest: English folklore, more or less as presented in the game—a goblin wolf creature.
Basilisk: medieval folklore
Behir: invented?
Beholder: An intellectual property of WotC (aka invented for the game), play on the proverb “beauty is in the eyes of the beholder”
Belker: invented?
Blink Dog: invented?
Bodak: English folklore (equivalent to Bugbear)
Bugbear: English folklore
Bulette: Saturday Night Live? (Candy-gram...)
Carrion Crawler: An intellectual property of WotC (aka invented for the game)
Celestial Creature (template): various mythologies
Centaur: Greek mythology
Chaos Beast: Cthulhu stories, apparently.
Chimera: Greek mythology
Choker: invented?
Chuul: invented?
Cloaker: invented?
Cockatrice: Medieval folklore
Couatl: Aztec folklore
Darkmantle: invented?
Delver: invented?
Demon: various mythologies/religions
Babau: Italian folklore?
Balor: Tolkein (Balrog), name from Irish myth
Bebilith: invented?
Dretch: invented?
Glabrezu: invented?
Hezrou: invented?
Marilith: Possible inspiration from Hindu Naga or Greek Echidna
Nalfeshnee: invented?
Quasit: Invented to be the demonic equivalent of the imp
Retriever: invented
Succubus: Medieval folklore
Vrock: possibly inspired by the Etruscan vulture demon Charun
Derro: based on the writings of Richard Sharpe Shaver
Destrachan: invented?
Devil: various mythologies/religions
Barbed Devil (Hamatula): Dante's Inferno
Bearded Devil (Barbazu): Dante's Inferno
Bone Devil (Osyluth): Dante's Inferno? invented?
Chain Devil (Kyton): invented? Spawn Comics?
Erinyes: Greek mythology, actually The Fates, not Succubi.
Hellcat (Bezekira): invented?
Horned Devil (Cornugon): Dante's Inferno
Ice Devil (Gelugon): Dante's Inferno? Invented?
Imp: European folklore
Lemure: invented?
Pit Fiend: Dante's Inferno? Invented?
Devourer: invented?
Digester: invented?
Dinosaur: historical
Dire Animal: pseudo-historical
Displacer Beast: invented?
Doppleganger: German folklore
Dragon: various mythologies
Dragon Turtle: Chinese mythology has a draconic turtle creature, but the D&D version seems similar to a giant turtle in the Arabian Sinbad legends.
Dragonne: I'd guess invented by TSR, as the toy Dragonne (tm) I had as a kid was trademarked.
Drider: Most likely invented when the Drow became more developed.
Dryad: Greek mythology, although Chinese legends also contain many tree-spirits that seduce mortals and die if their tree is killed.
Dwarf: Scandinavian/German mythology
Duergar: English folklore, possibly imported by the Normans from France/Spain.
Eagle, Giant: Tolkein
Eladrin: An intellectual property of WotC (aka invented for the game)
Elemental: Based on Greek philosophy of elements, only come to life.
Elf: Scandinavian/Celtic mythologies
Drow: Scottish folklore
Ethereal Filcher: invented?
Ethereal Marauder: invented?
Ettercap: Tolkein, The Hobbit, and linguistically similar to a Saxon small poisonous snake-man, the Attorcroppe (Little Poison Head).
Ettin: Scandinavian mythology, a linguistic variation of Jotun, or Giant.
Fiendish Creature (template): various mythologies
Formian: invented?
Frost Worm: invented? Possible Scandinavian origin
Fungus: invented, but based on actual fungi and slime moulds
Gargoyle: Medieval architecture
Genie: Arabian folklore
Ghost: various mythologies, the dead coming back to haunt the living is fairly universal.
Ghoul: Arabian folklore, a demon of wastelands that robs graves for food when there are no living victims handy.
Giant: various mythologies, again stories of really big people are pretty universal
Cloud Giant: Jack and the Beanstalk
Fire Giant: Scandinavian mythology
Frost Giant: Scandinavian mythology
Hill Giant: various mythologies, your standard “giant”
Stone Giant: Stone Giants throwing boulders in a thunderstorm are mentioned in The Hobbit.
Storm Giant: Greek mythology? They seem like a blend of Zeus and Poseidon to me.
Gibbering Mouther: Possibly inspired or taken from Cthulhu stories.
Girallon: Jethren believes this is inspired by a mythological monster, but the only information I could find (or Google matches) were d20 game links. I'm guessing it was made up.
Githyanki: An intellectual property of WotC (aka invented for the game)
Githzerai: An intellectual property of WotC (aka invented for the game)
Gnoll: Come from a story (or stories) by Lord Dunsany, according to Justisaur.
Gnome: French folklore
Goblin: European folklore, in general any malicious fairy is a goblin.
Golem: The original in Jewish folklore is the Clay Golem.
Flesh Golem: Frankenstein
other Golems: apparently invented to spice things up.
Gorgon: The name comes from Greek mythology (Medusa and her sisters were the Gorgons), but the bull form is possibly African in origin.
Gray Render: invented?
Grick: invented?
Griffon: Ancient folklore, related to the Sphinx, Mesopotamian Cherub, Lamassu, Manticore, and other “half-lion” creatures.
Grimlock: invented?
Guardinal: An intellectual property of WotC (aka invented for the game)
Hag: various mythologies
Half-Celestial (template): various mythologies
Half-Dragon (template): Apparently invented, I haven't come across any myths or legends of dragons spawning cross-breeds.
Half-Fiend (template): various mythologies
Halfling: Tolkein's Hobbits.
Harpy: Greek mythology
Hell Hound: British folklore, including The Hound of the Baskervilles by Arthur Conan Doyle. Related to Barghests, and the hounds of the Wild Hunt.
Hippogriff: Ancient/Medieval folklore
Hobgoblin: English folklore, another term for a goblin
Homunculus: Medieval folklore
Howler: invented?
Hydra: Greek mythology, see the Hercules legend.
Inevitable: Like many other planar denizens, I'm guessing this was invented.
Invisible Stalker: While invisible spirits and fairies are common in many myths and legends, this incarnation seems to be a TSR original.
Kobold: German folklore
Kraken: Scandinavian folklore (I double checked, and early written accounts come from Norway), and most likely inspired by actual giant squid attacks on ships. The Kraken in Clash of the Titans was Harryhausen's poetic license.
Krenshar: invented?
Kuo-Toa: An intellectual property of WotC (aka invented for the game)
Lamia: Greek mythology
Lammasu: Mesopotamian mythology, related to the Sphinx, Mesopotamian Cherub, Griffon, Manticore, and other “half-lion” creatures.
Lich: English folklore (the term is Old English) or maybe some Egyptian influence (undead spellcaster).
Lillend: invented?
Lizardfolk: A staple of D&D since 1st Edition, there are numerous humanoid reptiles in world myths and legends, but it's hard to peg one as the original Lizard Man.
Locathah: Possibly a variation of the mermaid, or maybe a creature from the Cthulhu stories. [The name seems similar to other Lovecraft names...]
Lycanthrope : European and Asian folklore
Magmin: invented?
Manticore: Persian/Indian/SE Asian folklore, related to the Sphinx, Mesopotamian Cherub, Lamassu, Griffon, and other “half-lion” creatures.
Medusa: Greek mythology, see the Perseus legend.
Mephit: invented?
Merfolk: Ancient/Medieval folklore
Mimic: invented?
Mind Flayer: An intellectual property of WotC with possible inspiration from Cthulhu stories
Minotaur: Greek mythology, see the Theseus legend.
Mohrg: invented?
Mummy: Egyptian/Universal Studios movies
Naga: Hindu mythology
Night Hag: English folklore
Nightmare: Possibly based on the mount of the Headless Horseman in The Legend of Sleepy Hollow.
Nightshade : invented?
Nymph: Greek mythology
Ogre: European folklore
Ogre Mage: East Asian folklore
Ooze: Based on actual corrosive molds and slimes, only on a bigger scale than normally found in nature.
Orc: Tolkein seems to have invented the humanoid form. Earlier references to a monster called an “Orc” seem to refer to killer whales (orcas).
Otyugh: invented?
Owl, Giant: invented?
Owlbear: invented?
Pegasus: Greek mythology, see the Bellerophon legend.
Phantom Fungus: invented?
Phase Spider: invented?
Phasm: invented?
Planetouched: invented?
Pseudodragon: invented?
Purple Worm: invented?
Rakshasa: Hindu mythology
Rast: invented?
Ravid: invented?
Remorhaz: invented?
Roc: Arabian folklore
Roper : invented?
Rust Monster: inspired by a '70s era “dinosaur” toy
Sahuagin: Possibly a variation of the mermaid, or maybe a creature from the Cthulhu stories.
Salamander: Ancient/Medieval folklore
Satyr: Greek mythology
Sea Cat: invented?
Shadow: invented?
Shadow Mastiff: Quite possibly linked to the Hell Hound/Barghest/Yelp Hound/Black Dog legends of England.
Shambling Mound: invented?
Shield Guardian: invented?
Shocker Lizard: invented?
Skeleton: various, props to Jason and the Argonauts for making them cool.
Skum: invented?
Slaad: An intellectual property of WotC (aka invented for the game)
Spectre: English folklore
Sphinx: Greek mythology, related to the Mesopotamian Cherub, Lamassu, Griffon, Manticore, and other “half-lion” creatures. The Egyptian monument was named the Sphinx by the Greeks when they saw the resemblance.
Spider Eater: invented?
Sprite: Medieval folklore
Grig: East Anglia (England), synonymous with Pixie
Nixie: German folklore
Pixie: Scottish folklore, likely a phonetic derivation from the Picts.
Stirge: invented?
Swarm: real life swarms
Tarrasque: French folklore
Tendriculos: invented?
Thoqqua: invented?
Titan: Greek mythology
Tojanida: invented?
Treant: Tolkein
Triton: Greek mythology
Troglodyte: Term for primitive peoples/cavemen. Not sure where the stinky lizard thing came from.
Troll: Scandinavian mythology
Umber Hulk: An intellectual property of WotC (aka invented for the game)
Unicorn: Medieval folklore
Vampire: Eastern European folklore, see in particular Dracula by Bram Stoker (as if you needed me to tell you that...)
Vampire Spawn: Eastern European folklore
Vargouille : invented?
Wight : The term is Old English for “man,” and the creature is based off of Tolkein's Barrow Wights in The Fellowship of the Ring
Will-O-Wisp: English folklore
Winter Wolf: invented?
Worg: Tolkein, The Hobbit and The Lord of the Rings
Wraith: English folklore
Wyvern: Welsh folklore
Xill: invented?
Xorn: invented?
Yeth Hound: Based on “yell” or “yelp” hounds of British folklore, in other words just another term for hell hounds or barghests.
Yrthak: invented?
Yuan-Ti: An intellectual property of WotC (aka invented for the game)
Zombie: Caribbean folklore, although tales of the walking dead exist the world over.
In Arabian folklore, ghouls were creatures prowling the deserts and eating unwary travelers. They had goat's legs or something like that which betrayed them to some. The keep-on-treaded-paths-or-be-eaten demon.
Excellent research.

My thoughts:

I believe gnoll also comes from English folklore. Just another bad spirit, ala bugbear.

There is a Lovecraftian creature of primordial ooze similar to the chaos beast, but it actually creates abhorrent little mud creatures, which break off and wander away. I think the chaos beast is supposed to be more resembling to the Thing, in the John Carpenter movie.

I could swear I stumbled across the word "derro" in something very pre-D&D, and it meant "dwarf." But I can't be 100% anymore. They did that with a lot of things. Adapting one word from one language for one creature, and then another that meant the same thing in another language, to represent, a similar creature or cousin to the other creature.

The word golem is Yiddish. It doesn't matter what type it is, since the word comes from the same place. Though, obviously, statues coming to life of various materials, such as the iron golem in Jason and The Argonauts, have been favorites in fantasy movies for as long as there have been fantasy movies.

Lich or lych is Middle English. It just meant "body" or "corpse." The lychyard was the cemetery.

Tolkien did not invent "orc." It's an Old English word for evil spirit.

There are lizard men in Conan tales, though not 100% sure in any of Robert E. Howard's original stuff. The original MM picture of a lizardman looks a lot like Spider-Man's nemesis The Lizard.

However, there are lizardmen and fish-men-like creatures in movies going back to the '40s. Probably most come from old black-and-white films.

The shambling mound is an obvious off-shoot of Man-Thing and Swamp Thing, both comic book characters. Troglodyte is a real word for "cave-dweller," but there was also a famous monster movie from the early '60s called "Trog."

And I would say Grimlocks are a copyright-friendly version of H.G. Well's Morlocks, from The Time Machine.
Formorian: From Irish folklore. One of those races who invaded/settled Ireland before the coming of the Celts. Succeeded the Tuatha de Danae and Milenesians, and preceded the Firbolg. Savage, primitive, disorganized. Largely supplanted by the more advanced Firbolg when they arrived.
Tried to post to this yesterday, it never got picked up. Let's try again. Great research!

A couple things to add:

Grimlocks are most likely the D&D version of morlocks from H.G. Wells' The Time Machine (they're pasty, unsophisticated, they're blind, they come from under the ground, and they eat people).

Troglodyte is a word meaning cave dweller, but there was also a movie from the early sixties called "Trog", that involved a monstrous cave dweller.

Lich, or lych is Old English for body or corpse. Thus, a lychyard was a cemetery.

The chaos beast bears a slight resemblance to something Lovecraftian, but to me it's more like The Thing from John Carpenter's version. There is a creature in the Cthulhu Mythos, I think it's Shub-Niggurath, that is like a black sludge deep within the earth, that creates different shapes, but these are like mud or tar creatures of primordial ooze that then separate from the main, to crawl off and either become awful things, or die. However, though I'm very well read in Lovecraftian works (both his and those of his compatriots), if anybody can direct me to a story with a creature very like the chaos beast, I'd love to read it.

Golem (actually goylem) is a Yiddish word that means shapeless mass. Yes, the original in the Ghetto story was made from clay. But does it matter? Any animated man-shaped thing is an offshoot. Though it's clear that animated statues have been a hit in fantasy films since there were fantasy films, such as the iron golem from Jason and the Argonauts.

Lemure is a Latin word for ghost.

I'm almost 100% sure that I've seen the word derro or something similar used in mythology somewhere, and that it simply was another word for dwarf.

ALL of the fish-men creatures in the game came from campy black-and-white monster movies, in my opinion. I've even seen outer space movies from the fifties with things that looked like chuul (only cheaper and sillier).

Lizardfolk in the original MM look just like Spider-Man's nemesis, The Lizard, though I am pretty sure there is something like them in a Conan story somewhere (but I don't think it's an original Robert E. Howard story). Likewise, shamblers are pretty much monster varieties of Man-Thing and Swamp Thing, both comic book characters.

Mephitis (from which I am sure they got mephit), is the stink you get around geysers and volcanoes.

Tolkien didn't invent orcs, per se, but did invent the way we view them today. In Old English, orc just meant evil spirit. I won't say demon, because demon just means spirit (implying power), and not all demons in all mythologies are evil (but being Catholic makes them so!). ;)

The Mummy was actually written by Bram Stoker, long before they made a movie about it. But actually, check out a book called In The Mummy's Tomb, which gives you various mummy short stories dating back to the early eighteen-hundreds, one written by Edgar Allan Poe.

Some words appear here and there in mythology in various forms, which were later borrowed. For instance, firbolg in the old 2nd-ed MM, is just another old word for giant. They do that a lot with D&D, using two words with the same meaning to denote two different, but often related, creatures.

And finally, though they did not call them drow, there is a race of dark elves in Scandinavian myth, as well.
Merfolk were from Greek first, children of Poseidon.
Nightmare was inspired by the Headless Horseman's horse.

#1. Dagon, the ancient Mesopotamian fertility/crop god, was depicted as half-man/half-fish. He was around before the Greeks. Talking 2,000 or so years before the Hebrews even showed up, or about 6,000 B.C.E.

#2. There are biblical-inspired paintings of wingless, black, flying horses fighting the forces of good across the sky, dating back hundreds of years.
The Rakshasha's name is from Hindu mythology, however, the idea of it being killed by a blessed crossbow bolt is from the television show Kolchak: the Night Stalker.
Merfolk: Medieval folklore

Finding some interesting stuff.

According to the wikipedia link above, one of the ancient Mesopotamian deities, Dagon, was sometimes portrayed as being half fish (possibly after having his name mistranslated).

http://www.pantheon.org/articles/d/dagon.html

http://www.pantheon.org/articles/d/dagon2.html

These people settled all over the Mediterranean, particularly noting Crete and Palestine, and would have influenced Greek and later mythos of the area.

Gnoll: invented?
Lord Dunsany

Possibly influenced by Set/Anubis or some other less well known Egyptian deity?
An allip is a type of ghost. I believe its Welsh.

Aranea are fairly obviously taken from the Greek myth of Arachne.

Darkmantles are actually an evolved form of the piercer, a monster from 1st ed. I believe that monster was based off of a piece of fantasy literature.

ALL the demons and devils that appeared in 1st Ed D&D (pretty much all of them on this list) have a distinct theological, mythological, or literary reference. In fact, it was these monsters, more than anything, that led to MMS (Mad Moms Syndrom) back in the 80's and forced 2nd ed to change the names to Ba'atezu and Tanari'i.

Ettercaps are Gaelic in origin.

If I recall correctly, Girralons are drawn from Moorcock's Stormbringer Saga.

The owlbear is an old folk tale from England, similar to Florida's skunkbear.

The D&D sphinx is Greek, not Egyptian, in origin. The Egyptian sphynx was named after the famous Grecian tale of a similar human-headed lion.

A vargouille is a type of vampire that traditionally was not undead and only fed when it left its body. There are variant vampires in most cultures, very few of which are dead or drink blood.

The wraith was a Tolkien invention. The word was meant to evoke certain feelings of dread within the reader.

Also, just because the most exposure to something you have had is SNL or Disney, don't make a listing like this and then throw something silly into it. Landsharks (bulettes) are an old sailor's fear, from what culture I'm not sure, that have been reworked. Cloud Giants are NOT from Jack & the Beanstalk! Hell hounds can be found in literature far, far older than Doyle's detective. And there have been stories of objects being brought to life through magic for centuries. (Although you are probably right about mummies having been included as monsters in D&D because of the Universal Studio movies from the 40's and 50's...)

The best way to start a list like this might be to look in the old 1st Ed MM and see what's in there. Gary & company drew heavily from mythology, theology, & literature. Even completely new creatures, like the mind flayer, had their roots in one of these sources (in the case of the mind flayer it's H.P. Lovecraft). Check out the 1st Ed core books for books to read. You'll recognize a lot of monsters from these books, even if the names are completely different. You'll also spend several months reading books that beat the hell out of anything coming out of Hollywood (except LotR & Narnia, of course).
Kuo-Toa: invented?

Also from Lovecraft, I think. Check out "The Shadow Over Innsmouth." http://www.dagonbytes.com/thelibrary/lovecraft/theshadowoverinnsmouth.htm

[N]o difference is less easily overcome than the difference of opinion about semi-abstract questions. - L. Tolstoy

The Nightmare is actually taken from Piers Anthony's Xanth novels.
The harpy also comes from Greek lore it may have actually been Homer who wrote of them.
IIRC, the beholder was specifically invented by Rob Kuntz.
Archons are Gnostic/Zoroastrian not Christian. Most "Celestials" are Babylonian including Deva, Seraph and Cherubim. The only truly original monster I can think of is the Beholder; of all the "eye monsters" I can find nothing resembles the Beholder.

"A truly creative person is one who is good at hiding his sources."
I've heard that the gorgon is used to mean two separate types of monsters in Greek mythology. The first are Medusa and her sisters, the other being the monster known as Catoblepas which according to myth breathed poison gas. The problem is Greek mythology isn't the most coherent group of stories. For instance the goddess Erinyes starts as a single entity and is then mentioned by Aeschylus as being three different creatures.

According to Dragon magazine, the Chuul, Kuo-toa, Shaugin, Mindflayer, Aboleth and others are based on Lovecraft.

The vampire and lycanthropes are found in pretty much every mythology on earth.
Archon: Judeo-Christian, some types possibly invented

Only in the very loosest sense. Of the Archons, beyond the name of the race itself, only the Trumpet Archons are directly taken from Xtian myth. The others are unique to DnD (beyond the names of the Tome Archons / Celestial Hebdomad)

Chain Devil (Kyton): invented? Spawn Comics?

They seriously predate the Spawn comics.

Erinyes: Greek mythology

Again, in name only. The Erinyes of Baator are quite different from the Furies of Greek myth, more like intellectual succubi than rampaging punishers of wicked mortals (the 3.5 changes to their abilities notwithstanding).

Lemure: invented?

Inspired from Roman myth. Lemures were the generic term for the souls of the dead, subdivided then into the Lares (benevolent) and Larvae (wicked).

Lich: English folklore?

The word 'Lich' comes from old English, but the creature is more likely derived from the Russian legend of Koschie the Deathless, a powerful sorcerer who could not die because he had placed his heart/life/soul within a magical acorn and hidden it where none would find it.
Shemeska the Marauder, Freelancer 5 / Yugoloth 10
This got me thinking so I wrote this, nothing really new and I get off-topic in a few places, but I enjoyed writing it, so maybe someone will enjoy reading it.

Ettercap: The name seems to based on the giant spiders in "The Hobbit", however, attercop is just an archaic (and according to Tolkien derogatory) word for a spider (also where we get the "cob" in cobwebs).

Kraken: Based on the Giant Squid, one of which was apparently observed live for the first time only just recently. The mythical beast referred to as a Kraken in nautical lore takes various forms, but the D&D creature is clearly of the squid-like variety.

Nightmare: Although, monstrous horses are a common enough mythological feature from the flesh-eating horses that plagued Hercules, to the Kelpie, to certain stories regarding the Picktree Brag and the Phouka, to the legend of sleepy hallow. However, since the D&D incarnation bears only the most rudimentary resemblance to any of these creatures I contend that this creature is simply a pun - like Mare Imbri from Xanth... but meaner.

Zombies: Stories of the living dead are found throughout the world the specific variety found in DND would seem to be based off bad 1950's horror movies. Which in turn are based on European perceptions of the religious and cultural practices of the Arrowak people. By the time the Spanish ceded Haiti to the French, however, the Arrowak were no more, having succumbed to smallpox and Spanish barbarity the survivors mixed with African slaves brought to replace them as laborers on the sugar plantations resulting in the people we now know as Creole. Many of these people were later brought to Louisiana prior to that states' purchase during the Napoleonic wars and afterwards spread throughout the southern states, which I presume may account for the prevalence of zombie stories in that part of the world.
This is a hobby of mine, to figure out the origins of D&D.
What you want:
#1 a copy of the 1st edition DMG
#2 a copy of the Dragon Magazine CD compilation
The first, at the back of the book, lists all the sources that Gygax used for creating 1st edition and has other insight into it's creation that is invaluable. The second allows you to quickly scan through 25 years of monsters being forged in the pages of Dragon magazine.
Here are some useful links as well:
http://www.sulerin.com/creatures/creatures.asp?op=index
http://www.geocities.com/rgfdfaq/sources.html
(this has the DMG list too)

I'll throw in a few more that I know off the top of my head as well right now.

Behir: Gygax, module the Lost Caverns of Tsojcath
Dire Animal: Conan, Robert E. Howard (has lots of them)
Frost Worm: Robert E. Howard's Conan
Ghoul: English folklore, Also Robert E. Howard for their sickly grey
Golem: Jewish folklore
Flesh Golem: Frankenstein
Clay Golem: Jewish folklore
Iron Golem: Robert E. Howard, Conan
Lich: Gygax. Taken from the word for the entry to a tomb.
Mind Flayer: Gygax. Inspired by artwork, see the stategic review.
Remorhaz: Gygax. Dragon 2.
Roper: Gygax. Strategic review.
Troll: THE D&D troll comes from 3hearts and 3lions by Poul Anderson. The word is much older, but the regenerating cave dweller hurt by fire is by Poul Anderson.
I have a suspicion that the Nazgul are an influence on the Lich. It's difficult to confirm; the similarities, though strong, are inexact. Magic in Tolkien is just different from DnD, which I think accounts for some of the differences.

The Beblith (Demon) is pretty clearly Sheilob. (I hope I spelled that correctly.) That's not to say that it lacks another ancestor; Tolkien obviously borrowed heavily himself.
Ghoul Arabian folklore indirectly flesh eating ghull
treant walking trees have been part of medievel British folklore since before medieval times
bodak unless I am extremely confused bugbears are the largest of the goblinoids and Bodaks are undead capable of killing with there looks
halfling mischievous little people wandering from place to place or living off the streets in huge cities have been around before Tolkien
couatl Toltec
aranea giant spiders have been around since ancient times
Lemure: Roman house spirit, not particularly important.
Remorhaz: Norse I think.
Sea Cat: Used to be a Sea Lion, monstrous version of a real animal.
Shadow: Bog standard thing.
Shadow Mastiff Black Shuck, English hell-hound thing.
Vampire: Everywhere has versions of this, Ireland has one of the oldest versions of the immortal blood-drinking type.
Vargouille:One Indian version of the vampire I think.

Apart from that a lot of the things listed as medieval by the first poster tended to turn up in classical writings so they definitely predate the dark ages at least.
Orc
This is an odd case. Latin had Orcus which essentially meant "demon". There are various references (many in Italian) from classical times up until Tolkien's use of the word in his own books. Now, his books are also referenced regarding the word.

The odd thing? Tolkien spent several years working on the staff of the Oxford English Dictionary . Which is where I found those references. How many authors served on a staff of such a prestigious publication, only to later be a subject of reference in its own pages? And one thing to wonder about; did Tolkien himself write the original entry for Orcs?
Ah, found some more information.

Mind Flayer: possible inspiration from Cthulhu stories?

On this matter, Gary Gygax says: Well...
No need to speculate, for I can set forth the process in a few words. Larry Niven's writing had nothing to do with the creation of the Illithid race for the AD&D game.

I happened to be thinking of devising a new terrible race if creatures inimical to humans, and my eye fell upon a paperback book authored by Brian Lumley, The Burrowers Beneath. The cover illustration was of a bipedal monster with a head resembling a squid or an octopus. Voila!

http://www.enworld.org/showthread.php?t=125997&page=42&pp=40

And, regarding Drow/Kuo-Toa:
BTW, the drow were inspired by no more than a dictionary listing for the name as "dark elves," and I made up the kuo-toa out of whole cloth so as to have another underground race on distinctly non-human sort.

Great work!!
The Gorgon of Greek Myth was a bull. The Medusa poured out of the dead Gorgons neck.

Someone else pointed out the error here, but I just wanted to elaborate slightly.

In Greek myth there were three monstrous sisters who were so ugly none could look at them without turning to stone. They were called the Gorgons. Their names were Stheno, Euryale and Medusa. As has been noted, Medusa was mortal and ended up killed.

But there are also myths about a metallic bull that never raised its head, because those who saw its eyes died instantly. The two myths have become confused slightly when imported to D&D, which has a tendency of making singular monsters into races. A recent Dragon magazine actually had an interesting article about this very issue, with references to other sources.

But another monster fits into this story: The Pegasus. When Medusa was decapitated the first Pegasus sprouted from her blood. It could be this story that someone confused with the story of the metal bull.
The original form of the Bulette came from the same package of 70s-era "Dinosaur" toys that the Rust Monster came from. I should know, I had that set of toys. :D