Dungeons & Dragons is one of the greatest games of all time. I might be a bit biased in saying that, because I've made a living out of writing RPGs, including having been involved with the creation of the latest edition of D&D. But you don't have to take my word for it; just a short while ago, D&D was inducted into the "Toy Hall of Fame"!
It's also had a huge effect on pop culture. Most modern fantasy stories have drawn inspiration from D&D (like D&D itself drew inspiration from earlier fantasy literature as well as ancient mythology). And most video games, especially those with fantasy elements, have borrowed a lot from D&D too. And literature, films, and TV (Game of Thrones being an obvious choice).
So, in celebration of D&D's history and it's rebirth, here's a list of some of the most famous (and dangerous!) monsters that either got their start in D&D, or were redefined by D&D. They're presented in rough order of badassity.
1. The Drow
There were dark elves before, but nothing quite like the Drow from D&D. A matriarchal race of totally evil underground elves worshiping a spider-goddess, you really don't get weirder elf than that. The Drow appeared relatively early in D&D's history: they were mentioned in the first Monster Manual, but weren't given statistics there. They first appear with statistics in the adventure "The Hall of the Fire Giant King". But the Drow wouldn't rise to their enormous fame until the Forgotten Realms setting came along, and specifically a series of novels starring Drizzt Do'Urden, the renegade good Drow who became one of the most popular heroes, and one of the most unbearable Mary-sues, of hundreds of bad D&D novels (or at least, it feels like there's been hundreds of them, maybe it's only dozens). Like most D&D elves, the Drow are capable fighters and also powerful magic-users, but the Drow are also evil and dark and often brooding, which makes them highly attractive to teenagers and other immature personalities.
When dark elven spider-cultists became too banal, D&D introduced the Tieflings. These are
"half-demons", which were created as a player race (that means, you can play a tiefling in the game). They came along in 1994, and quickly became the favorite of people even more insufferable than the ones who always wanted to play "a drow with two scimitars". Their most fundamental power is that they look weird and normal people don't like them, which for some reason struck a real chord with some geeks, not sure why.
OK, now we're getting somewhere! The basic thing about owlbears is that they're like a bear, but also like an owl. The venerable owlbear is one of the oldest D&D monsters, dating back to 1975; it was apparently inspired by a weird toy that D&D-creator Gary Gygax once owned. This animal-intelligence monster has been a staple of D&D ever since, and a favorite of forest-encounters for sadistic Dungeon Masters everywhere. It's an owl, it's a bear, what's not to like?
The Bulette was another terrifying monster for wilderness encounters. It was described as a "land shark", and it was seriously freaking deadly. That's right, D&D had deadly sharks on land decades before the Syfy network existed!
It actually burrows under the earth, attacks you by surprise, has multiple attacks, and heavy armor. Like the owlbear, it too was inspired by a toy monster Gary Gygax once owned; and first appeared in 1976. It was just one "fly" spell away from a direct-to-video blockbuster.
5. Displacer Beast
Yet another great character-killer, the Displacer Beast first appeared in 1975, and is a kind of panther with six legs and a pair of tentacles. But if that wasn't dangerous enough, the reason they're called 'displacer beasts' is that they appear to be a few feet away from where really are; this makes them very difficult to hit. They come from another plane (which is D&D-talk for 'dimension'), and they are the hated enemies of a way lamer creature called the 'blink dog', which is really just a kind of dog that can teleport. Seriously, Gygax? You come up with a six-legged tentacled panther with predator-powers, and the best you could come up with as their nemeses are "dogs that can teleport"??
6. Gelatinous Cube
There's two things you need to know about a Gelatinous Cube: first, that it's a cube. Second, that it's gelatinous! The Gelatinous Cube was introduced all the way back in the very first D&D rule-set in 1974; it was created as one of a number of monster-concepts answering the all-important question of "what keeps all those dungeons clean"? The answer was a 10-ft cube that would slowly move through dungeon corridors, which dissolves all organic matter it sucks into itself. It's totally quiet, and of its own is completely transparent, meaning you only have a chance of really noticing it's there if there's a half-dissolved corpse (or non-organic remnants) floating around inside it. Note that most dungeon-corridors were also 10x10, meaning that the cube would completely occupy the corridor, making it very tough to avoid!
There were a number of other slimes, oozes, and even the dreaded black pudding in the list of classic dungeon-goos. It's led to a long-standing pair of rules for adventurers: #1, make sure you can tell the difference between 'good slime' and 'bad slime' (if it moves or glows, it's definitely bad slime!). And #2, don't touch any substance you aren't absolutely sure is 'good slime'.
7. Rust Monster
A gelatinous cube or green slime could kill you in horrible ways, but a rust monster was even worse: it couldn't physically hurt you at all, but it could ruin all your stuff! First appearing in 1975, the Rust Monster was a creature specifically designed to take away your character's weapons and armor, which proves what a dick Gary Gygax (and from him, all future Dungeon Masters) could be. The Rust monster looked like some kind of weird lobster-armadillo, and any metal object touched by its antennae would rust away to nothing. It could even affect magic weapons or armor, which made it a truly hated creature for any characters loaded up on high-powered gear. It was yet another creature inspired by a toy Gygax owned. Those toys have a lot to answer for.
Mimics weren't based on a toy, since they don't have any fixed appearance at all. It was monster made to surprise adventurers, and often to play on their most basic motivation: greed. Mimics can shapeshift to take the form of ordinary objects: tables, chairs, and doors, for example... but most often, treasure chests! When someone touches a mimic, they get stuck to it, and then it grows a kind of meaty fist to beat their victim to death with, after which it will eat them. Encounters with mimics have been more responsible than any other monster for turning adventurers into neurotic basket-cases suspicious of any everyday object they find. All those sensationalistic tv-movies from the 1980s might have been on to something after all: dungeoneering is not good for your mental health!
Of course, giants have been around in mythology and fairy-tales since way before D&D came along. But the D&D game developed a whole new ecology of giants that affected later fiction. One of the things that really motivated their popularity as monsters (dating back to the original 1974 rules) was their division into different 'races' of giants: Hill Giants, Stone Giants, Fire Giants, Frost Giants and Cloud Giants. Each of these ranged in size (from the 10+ft tall barbaric Hill Giant, to the enormous 20+ft tall Storm Giant). They also varied in personality; some were evil and stupid, others highly intelligent, a few were even good.
They became even more popular after a series of early D&D-Adventures collectively titled "Against the Giants". A variety of other types and sub-classes of giants appeared in later adventures and supplements. Mainly, though, they existed as a really-tough non-dragon opponent, and a source for players to bitch at their Dungeon Master about putting one in a dungeon room when he can't fit through any of the entrances.
Included on the list mainly because of how damn weird they are, the Xorn are bizarre-looking creatures from the "Plane of Earth". They can phase right through stone or rock, and they eat precious metals (like all those coins your adventurers have been collecting in the dungeon). They date back to 1977, to the first Monster Manual. They're best known among players as "what the fuck is that thing?!"
There's few absolutely original monsters that D&D came up with that more caught the imagination than Beholders. Apparently a totally original invention, the "Eye Tyrants" are a race of very intelligent evil creatures shaped like a big floating eye with a bunch of tentacles that also have eyes, and all of the eyes fire different deadly magical rays. What's not to like?
On top of it all, their big central eye cancels out magic, making them incredibly tough to fight because unless your wizard can somehow get behind the beholder, he's useless. In spite of being pretty goofy looking, especially in the early illustrations, Beholders have only become more and more popular over the years, with a ton of variants being designed to keep adventurers on their toes.
While not entirely original, D&D helped remake our ideas of elementals. In ancient myth these were often wise nature spirits or the like. In D&D, they're creatures, made of pure Air, Earth, Fire or Water (there are also weird variants of all kinds, like Ice Elementals, Smoke Elementals, etc.), that come from the "elemental planes". They're often conjured up by wizards to act as guardians, and if adventurers are very lucky they might be able to gain magic to control them too. They come in various sizes, and are generally very tough opponents. Instead of wise or intelligent nature-spirits, D&D elementals are usually just big dumb hulk-like killing machines.
The D&D concepts of Elementals has spread out all over the place into popular fiction, and other video games.
The Otyugh is a weird, lumpy 500lb monstrosity with an eyestalk and spiked tentacle, surrounded by filth and covered in shit. It's another original D&D creation, dating to the first Monster Manual (though I think it might have had some inspiration related to both Lovecraft and the trash-monster in Star Wars). It was another creature designed to explain the ecology of dungeons and caverns adventurers explore: the Otyugh is the garbage-eater of the dungeon, found in the filthiest places. But while crap is its main cuisine, Otyughs have no problem snacking on the occasional adventurer too. It's the monster you add to the dungeon if you want things to get really disgusting.
Rakshasas are described as "evil spirits" who are "fond of a diet of human meat"; they're also immune to all but the most powerful spells and magic weapons. But that's not what made them cool. That picture, the picture that came with them in the original Monster Manual of the tiger-dude smoking a pipe, that's what made them freaking unforgettable!
I could go on about their abilities or qualities, but the whole appeal of this monster is really just "Tiger Dude Smoking a Pipe!!"
Rakshasas are very loosely based on a monster based on Indian mythology, very VERY loosely; but I'm pretty sure that was just a cheap excuse to have a tiger dude smoking a pipe. A far more accurate depiction of Rakshasas would appear in my own Indian-based RPG book, Arrows of Indra, and you'll find they don't have much in common with the monster from the original D&D manual. But you really can't beat the coolness of that image.
15. Umber Hulks
This gruesome monster was a large bipedal insectoid creature capable of digging through solid rock with its powerful mandibles. To make things worse, not only are Umber Hulks tough, but their gaze can leave adventurers dazzled and confused. And of course, humans are listed as one of their favorite snacks.
I'm not quite sure what makes Umber Hulks special, but they definitely tap into something. They're kind of like the Bulette in that sense: the Bulette is the Land-Shark, and the Umber Hulk is like the Land Shark of the Underground.
16. Mind Flayers
Mind Flayers, or Illithids, are one of the most iconic truly-original D&D monsters. They're clearly inspired by the kind of horrific things you see in H.P. Lovecraft's "Cthulhu Mythos" stories, but they are presented in an original way. Mind Flayers first showed up in 1975, and were a very evil very alien civilization that lived very deep underground. They have psychic powers that can be used to disable adventurers; and once they've done that, their tentacles can burrow into a human's skull to eat their delicious brains.
The reason mind-flayers work is why all the Cthulhu stuff works: tentacle-terror. Add in that they're the only major monster to use Psychic Power instead of magic power, and it was a recipe for success.
OK, so there's been a lot of weird monsters in this article so far, but the Catoblepas may very well be the weirdest of all, as well as the most deadly. In the original Monster Manual it's described as having the body of a "huge, bloated buffalo" with thick stumpy hippo-like legs and an "offensive odor". It has an elongated neck and the face of a hideous warthog. The most dangerous thing about it is that its gaze causes instant death, no "saving throw" allowed!
The Catoblepas is just too strange, even for the imaginations of D&D's very imaginative creators. It's actually based on an ancient myth, described in the writings of the great 1st Century Roman naturalist, Pliny the Elder. According to Pliny, the Catoblepas was a real animal that lived somewhere in modern-day Ethiopia.
On the whole, this is not a creature that in my D&D experiences is often encountered. It's just too dangerous. There's nothing that would piss off even the most reasonable player than "hey look there's a water buffalo... and now you're dead. No, you don't get to roll anything, you're just dead".
The undead are a prominent feature of D&D at any level of play. Adventurers face skeletons and zombies from the very start of their careers, and later wights, wraiths, mummies and vampires, among others. But the Lich is pretty much the toughest undead opponent there is. Unlike the lesser undead, Liches are intelligent, highly intelligent. They were wizards in life, who used dark sorcery to obtain eternal (un)life; as undead they are still powerful wizards. Their souls are placed in an artifact called a Phylactery, which means that even if you manage to destroy their powerful bodies, they can just return to life unless you find and destroy the depository of their soul.
Liches were based on ancient legends of the living dead, and inspired by early fantasy fiction from Ambrose Bierce, Clark Ashton Smith, and others. But the D&D version of the Lich, first appearing in 1976, ended up inspiring a number of later fantasy creatures.
They're undead, they're super-evil, they have magic, they're really smart, and they don't have all the weaknesses that make Vampires easier to kill off. The phylactery is what tops it all off: it gives you a villain that your players can kill over and over again and he'll just keep coming back to screw with you again.
19. The Demogorgon!
If you've watched Stranger Things, you've heard about the Demogorgon. But you might be wondering just what the hell it is. Yes, it's a real D&D monster, but it's not a 'type' of monster, it's a single dude, a super powerful Demon Prince. The Demogorgon is a super-powerful enemy, with 200 hit points (that's a lot), incredible armor and resistance, a hypnotic gaze which also causes insanity, his attacks can dismember your limbs, and he has a bunch of spell-like powers on top of that.
Contrary to what the Stranger Things kids led you to believe, a Fireball won't do shit to the Demogorgon, so don't be misled! If you face this guy, odds are you're toast. Especially if your adventurer is named "Barb".
You can't really make a list of the most famous Dungeons & Dragons monsters without including Dragons. Obviously, dragons have been around since way before D&D. But like everything else it touched, D&D put its own very influential twist on these ancient monsters.
In D&D, dragons are divided into (mostly evil) "chromatic" dragons (red, blue, green, black and white dragons being the most common) and (mostly good) "metallic" dragons (brass, bronze, copper, silver and gold). The good dragons are ruled by the great Platinum dragon Bahamut; while the mother of evil dragons is the five-headed Tiamat, who rules "the first plane of the Nine Hells".
There are both intelligent and non-intelligent dragons; intelligent dragons can cast spells. All dragons have some kind of terrible breath weapon, the type of attack depending on the type of dragon (red dragons breathe fire, blue dragons breathe lightning, white dragons breathe cold, etc.). Dragons can detect most kinds of hidden or even invisible creatures, and large dragons cause terror in lower-level humanoids. They're meant to be incredibly tough opponents, but of course they also have huge treasure hordes, which is why we can't stop delving into those dungeons to find them.