"And was this fellow, Oz, a powerful dinh? A baron? Perhaps a king?" Again, the three of them exchanged a glance from which Roland was excluded. "That's complicated," Jake said. "He was sort of a humbug—" "A bumhug? What's that?" "Humbug," Jake said, laughing. "A faker. All talk, no action."
In the Cowboy Bebop episode "Brain Scratch," the mysterious and sinister Dr. Londes turns out to be an internet persona created by a paralyzed and semi-comatose teenaged boy in a hospital.
While his People Puppets are incredibly powerful, and he is capable of unbelievably terrifying deeds by proxy, Nagato, AKA Pain turns out to be...a withered near-skeleton of a man incapable of standing upright or moving on his own and constantly at death's door.
In Afro Samurai (manga only), Afro has murdered his way through the ranks of those who either covet his Number 2 headband or are protecting the current Number One, only to find that his target died long ago.
This happened in the game version as well, but ended in such a way in that there was a still a satisfying Final Boss fight.
Yellow Claw in Agents of Atlas turns out to just be a feeble, dying old man whose schemes turned out to be just a desperate publicity stunt to advance the career of his chosen heir.
In "The Hard Goodbye", the first Sin City story, Marv kills his way through hitmen, gangsters, a police death squad and a silent and deadly farm boy cannibal killer to get to the man behind the murder of Goldie...who turns out to be a really little old man who isn't nearly as imposing as his fearsome reputation as a Cardinal would lead one to believe. The big bad cowers and dies screaming as Marv exacts his revenge on him.
The infamous Adversary in Vertigo Comics' Fables turns out to be... Geppetto, still as happy and kindly as ever, but turned megalomaniacal after he was requested to help overthrow and replace one too many evil dictators with wooden stand-ins from his magic grove (the same one he carved Pinocchio out of). While he's gathered quite a gaggle of evil Fables under his thrall, without his authority and his magic wood, he's actually quite pathetic.
Mr. Mind: The head of the Monster Society of Evil turns out to be an intelligent bespectacled worm. Not a big worm, or even a mind controlling worm (that's retconned in later) but a normal sized green worm. With glasses. Kids must have laughed...
The retcon makes him terrifyingly powerful. His normal form is telepathic and telekinetic, while his evolved form eats entire universes.
Early on in the Deadpool Corps series, the Deadpools have to stop The Awareness, a cosmic entity resembling a giant cloud that is feeding on the minds of entire alien species and making them its slaves. Actually, the real Awareness is a pretty pathetic-looking little alien, the huge nebula being nothing more than a shroud. Once the Deadpools make it past his minions and his traps, he is easily dispatched.
Oz: PAY NO ATTENTION TO THE MAN BEHIND THE CURTAIN!
Though, uncaracteristically for this trope, he is not really a villain.
In Equilibrium, Brandt is initially depicted as a competent foe able to keep Preston on the ropes during a practice spar. When they fight for real, however, he dies in three of Preston's invisibly-fast strokes before he can even move to defend himself.
Subverted immediately afterwards: Big Bad DuPont, who appears to be a harmless bureaucrat, proves competent enough in Gun Kata himself to fight Preston in single combat pistol-against-pistol, and lasts longer than all the previous well-armed mooks combined.
Subverted in Ultraviolet, also directed by Kurt Wimmer, where Vice-Cardinal Ferdinand Daxus also initially seems doomed to a quick defeat but proves an able combatant against Violet, who has thus far been virtually unstoppable.
Halfway through M Night Shyamalan's The Village, we discover that Those We Do Not Speak Of, the bogeymen who hold the entire village in fear, are merely a ruse by the elders to keep the people in line. This is subverted when Ivy is let in on the secret and is attacked by one of these creatures anyway. And then that is subverted when we (but not Ivy) see that the creature was actually the town's Ax Crazy man in a costume.
Jigsaw from the Saw series has a reputation as a dangerous murderer, but is revealed to be a fairly weak man with brain cancer, only able to operate because of his manipulative skill.
Done literally in 10,000 B.C. - we only see the man in question for the briefest of moments, but it's long enough to confirm that not only is he not a god, but he's a pasty old white guy.
The 1989 version of Batman. When Batman finally confronts the Joker at the top of the Church he beats the everloving shit out of him with no trouble. It's only when Batman attempts to save the Joker from dying that there's trouble. Contrast this with the 2008 Joker/Batfight where even though the outcome is largely the same, the Joker still gets a few good pipe shots in.
In Crank High Voltage, the man who stole Chellios' heart (and whom narrative convention would suggest is the Big Bad) is the legendary leader of the Chinese Triads, played by David Carradine. About 2/3rds of the way through the film he's revealed to be a wizened Dirty Old Man who has about 2 minutes of screen-time and is promptly and anticlimactically lured to his death by two odious comic relief characters. The film's real "Big Bad" is a completely unrelated, entirely different character who seemingly comes out of nowhere in the final reel.
Star Wars: Return Of The Jedi subverts this — we're meant to think of the Emperor this way, as being unbelievably sinister despite being totally helpless and weak, right up until he suddenly unleashes the Force Lightning. (This is a great cinematic moment that has been totally diluted for modern audiences thanks to the proliferation of Force Lightning in the video games and such.) The Emperor seems set up to be Yoda's opposite. Physically unimposing, but near God-like powers when he actually chose to use them. One of the Star Wars RPG books speculated that a no holds barred Jedi duel between Yoda and The Emperor could devastate a planet. The actual fight only thrashed a building, but was nevertheless awesome.
One Expanded Universe novel sums up the precise nature of the Emperor quite well in a short description: "A shell of a human in a hooded cloak... more energy than flesh". Sure, his physical form is weak and unimpressive- but he's so far gone into The Dark Side that this form isn't even the "real" him any more, just the shell that holds him.
The shell concept becomes more literal in the expanded universe when the idea was introduced that Darth Sidious' long life was achieved by transferring his consciousness from one cloned body to another.
In Iron Man 3, The Mandarin turns out to simply be a figure fabricated by Aldrich Killian, with the man himself simply an actor playing a role in exchange for a comfortable lifestyle.
The trope title and the page quote both refer to Oz, the Great and Terrible, who, as everyone now knows, proved to be neither. While in the film his disguise was a fiery hologram, in the book he changed disguises every day. (A giant head, a beautiful woman, a dragon, and a fireball.) In the sequels, though, he does become a bona fide wizard.
Malkariss, ruler of the subterranean kingdom from the Redwall novel Mattimeo. He spends his life inside a giant carving of a polecat that amplifies his voice. He's really so old that he's practically helpless when his own slaves attack him.
Randall Flagg, Mordred Deschain, and the Crimson King from The Dark Tower. Stephen King even foreshadows this in the quote at the top of this page, which occurs right before a scene in which Flagg reenacts the exposing of The Wizard of Oz.
Flagg and the Crimson King are two cases where The Man Behind the Curtain overlaps with Villain Decay. In previous novels like The Stand and Insomnia, they were presented as competent and terrifying, but Stephen King subsequently changed his mind about the nature of evil and set these villains up to be exposed as humbugs in the final volume of The Dark Tower.
The Star Trek novel Kahless is, essentially, a "demythologization" of the Klingon legends about the titular character. When Kahless finally confronts his traditional enemy, the tyrant Molor, he discovers that Molor is not an invincible warrior—just a dying old man.
Mr. Foreclosure, the villain of The War Between The Pitiful Teachers and the Splendid Kids, is an ant. Not even a giant ant.
In Lady Knight by Tamora Pierce, Blayce is called "The Nothing Man", because that's what he is: a short, weak, fidgety, acne-ridden slimeball. And yet he killed hundreds of innocent children to fuel iron killing machines with their souls...
Werner von Aargau in Tim Powers' The Stress Of Her Regard. His contract with the nephilim - having one of them physically implanted in his body to link their species with humanity - has kept him alive for the last several hundred years, but didn't stop him from aging. He is now spliced into the fabric of a building in such a way that he cannot be killed without Taking You with Me.
The demon Quetzovercoatl in Terry Pratchett's Eric. The Nightmare Fuel demon who's the basis of an entire warlike religion turns out to be all of six inches tall. To add insult to injury, he's killed seconds after appearing on earth.
The Authority in His Dark Materials is revealed to be a frail, old and hopelessly senile angel sealed inside an almost indestructible crystal cage by his servants to keep him alive. He's even lost the ability to speak, but seems happy when the protagonists unwittingly kill him without even realizing who he is.
Cronal from the Star Wars Expanded Universe is a subversion- he hides behind holograms and body doubles to disguise the fact that physically he's a frail old man on life-support, but he's such a powerful darksider that he doesn't need a working body to kill you.
The Tooth Fairy in Hogfather, although it's not precisely villainous.
In Barbara Hambly's novel The Ladies Of Mandrigyn, the whole world fears Altiokis the Wizard King, shadowy ruler of a mighty empire, the greatest wizard the world has ever known, immortal, invincible... It turns out he's a third-rate magician who captured something by luck in his youth; by some combination of his own cretinous nature and the mind-corroding effects of the alien power, he's become a vicious, dull-witted, infantile glutton who whiles away the centuries indulging his base appetites.
In Jeff Somers's cyberpunk novel The Electric Church, the leader of the eponymous Church (which offers "salvation through immortality" by means of cyborg conversion) is a digitized consciousness in a box (though his personal avatars, the Cardinals, are very formidable).
Live Action TV
In the Halloween episode of Buffy the Vampire Slayer, "Fear Itself", Buffy and company must fight their way through a haunted house where the decorations have been brought to life as monsters by the influence of Gaknar, a primordial fear demon. When the demon itself is brought forth, it is so tiny that a fearsome-looking picture of it shown earlier proves to be actual size. There's an Aesop — the standard "The only thing to fear is fear itself" moral, hence the title.
LOST's Jacob, who runs the Others from a secret cabin and can apparently only speak to Ben, is such a straight execution of this trope that the episode in which Jacob first appears is in fact titled "The Man Behind the Curtain."
Subverted: There was no man behind the curtain - Ben never spoke with Jacob, who doesn't really live in the cabin. Whoever Locke heard, it wasn't Jacob...and he wasn't in charge. The actual Jacob appears only two seasons later.
It turns out it was actually Jacob's brother, who is actually the Black Smoke, which means it's subverted to hell and back as it's therefore the Unkillable Monster behind the curtain. Just to rub salt in it, the image that Locke sees in that chair is actually a vision of his dead self, a reference to the Monster plotting Locke's death. Jacob did use to live in that cabin, and the Monster is old and manipulative enough to really be in charge, in a sense, even if nobody realizes it.
Star Trek' Balock, from the episode "The Corbomite Maneuver," has the appearance of a human child. When he communicates with other ships via the viewscreen, he uses an intimidating puppet.
The Feeble Files adventure game has one of these, although it's not a person who you'd know about before you reached the final "dungeon." The CEO of Omnicorp, the man behind the Omnibrain, the ultimate source of all the torment in the galaxy is a senile old guy who was actually asleep for the last several centuries while a strategy game AI ran things for him. He dies instantly when a frustrated Feeble punches him in the face.
Emperor Murod in the original Summoner, despite being served by legitimately intimidating and nasty lackeys and being responsible for actions of gross evil... is just a feeble old man. On top of this, he's an Anticlimax Boss, even after pulling a One-Winged Angel out of nowhere.
Subverted in Advance Wars - Dual Strike with CO Von Bolt, a feeble old man. But since all of the actual combat is between replacable mooks, and Von Bolt is a strategic genius with a devastating CO Power, he's still pretty threatening.
No More Heroes 2: Desperate Struggle is all about Travis fighting his way to the man responsible for the murder of Bishop, Jasper Batt Jr. By the time you reach him, he reveals himself as a tiny, weak, buck-teethed man who is only capable of fighting you with his rocket-racecar-desk and robotic bats.
Though this is subverted rather gloriously as after he is first beaten he pumps himself full of steroids transforming into the hulking Batt-man. And if you can beat that, he somehow bloats up to the size of a blimp to crush Travis.
In Darkened Skye, the Big BadEvil Overlord Lord Necroth is widely known and feared as "He Whose Face Must Not be Glimpsed". It turns out that Necroth is really an inch-high maggot using a giant megaphone to communicate with his followers. Skye even has to use a shrinking spell to enter Necroth's throne room to confront him. Skye even remarks "He Whose Face Must Not be Glimpsed. That's because he's too small to see! You're Lord Necroth? You're nothing more than a pathetic little..." Despite being The Man Behind the Curtain, Necroth is not an Anticlimax Boss, as he does put up a reasonable fight (since the heroine is also only an inch high at that point). Possibly a Shout Out to Mr. Mind, above
In Final Fantasy X, The Man Behind the Curtain, Yu Yevon, is described in the third act to be the controller of Sin. This feat gives the impression that his power must be immense, yet he is revealed in the final battle to be nothing more than an insect. A spectral insect, but an insect nonetheless.
Most of his feats were done in ages past, and he's degenerated so much he's really quite defenseless on his own. In his prime, however, he was likely the greatest summoner the world has ever known and created TWO Epic Level Summons with his skills. At the same time. He's also the father of Yunalesca, another contender for being the greatest summoner since she created the Final Aeons, another Epic Level Summon AND she knows how to make more of them if need be. After 1000 Years of Epicness, it seems to have finally decayed Yu Yevon utterly.
The Collector in Little Big Planet (not to be confused with thoseCollectors) spends the entire game one step ahead of the player, hiding in the background and snatching away various objects and NPCs with a giant robot and an Evil Laugh. Once you've finally chased him to his bunker and defeated his robot, however, he turns out to be a tiny little guy - smaller than Sackboy, even - and all he really wanted was some friends. Needless to say, he's immediately forgiven, and everything ends on a happy note. What kind of game did you think this was?
Parodied in one of the joke endings of Silent Hill 2, where it is revealed that the unseen entity jerking James around and forcing him to relieve the most painful memories of his life is...a shiba inu dog. Roll credits!
Fallout New Vegas has Mr. House, the enigmatic genius who controls the Vegas Strip with his army of robots, who nobody has ever met in person and is rumored to be the oldest political force in the Mojave Wasteland. He turns out to be a shriveled, almost-mummified 261-year-old Howard Hughes Expy sealed in an iron lung, who dies of multiple viral infections if you so much as open the case he's shut in.
The "Old World Blues" DLC has Dr. Mobius. In his introduction, he comes off as a psychotic Mad Scientist bent on destroying the Think Tanks with his intelligence-draining Robo-Scorpions. When you finally meet him, he's a cripplingly senile junkie and a kindly, grandfather-like brain who relies on drugs to gather up the aggression to broadcast said message and whose plans are focused on keeping the Think Tank in Big MT so that they don't the world outside their personal testing facility.
Mad Mod in Teen Titans turns out to be a feeble old man running a simulator. The version they were going after was actually a hologram.
Subverted by Brother Blood, who looks like a frail old man relying on personal charisma and Mind Control powers to make himself seem dangerous- and then Cyborg gets into a fistfight with him, and he turns out to be one of the most dangerous hand-to-hand combatants in the show.
Mr. Big in Rocky And Bullwinkle always cast an enormous shadow because of a flashlight he always kept with him, but ended up being one or two inches tall, and can be picked up with two fingers. It is later revealed, in his last appearance, that not only is his shadow effective enough that he can take over the moon with it, he is still strong enough to beat up a full-sized person.