Fake King

"Fake King Plot: Oldest RPG subplot known. A town has a fake king that is really a monster, while the real king is imprisoned. Sure signs you're dealing with a Fake King Plot are messages like "The king has been acting strange lately" or "The king hasn't been himself since ..." References to this plot have even been found in primitive cave paintings."

- The RPG Cliches Game

"My noble half-brother whose throne I usurped will be killed, not kept anonymously imprisoned in a forgotten cell of my dungeon."

- The Evil Overlord List, Rule #3

Rarely seen in the same country as the Evil Chancellor and rarely a Final Boss -- though they can be a significant one -- a good, often beloved ruler or other authority figure has been replaced by a doppelganger of some kind with horribly evil intentions. The Fake King exploits the country's people and resources to further his nefarious agenda. He often isn't very subtle, but you don't get much in the way of disobedience except from the heroes; everyone else just remarks on how the king is acting funny or has changed. The replacement usually happens before the story starts. It could be seen as the lazy way to become a Villain with Good Publicity, or for the Evil Twin to star in a Tyrant Takes the Helm story. Many Role Playing Games use this setup and the inevitable exposure of the usurper and restoration of the real king as a rather forgettable Fetch Quest. (For some reason, the usurper never takes the advice of the Evil Overlord List item quoted above and resorts to just killing the king to really complicate the matter.)

While this specific Fake King plot is arguably a Dead Horse Trope in console RPGs by now, the general trope of replacing a good authority figure with an evil one through Voluntary Shapeshifting, possession, the existence of an Evil Twin, cloning, illusion magic, or some other form of Applied Phlebotinum is considerably older and potentially more varied. The key points are that the authority figure is known as a real person and that he or she gets replaced by a look-alike who makes things worse -- a villain disguised as the king.

If a hero stands in for the king, it's Emergency Impersonation.

Anime and Manga

 * In One Piece, Mr. 2 Bon Clay impersonates the king to get everyone in Alabasta to fight. Only one kid notices this, and he's too injured by Baroque Works to tell anyone.
 * In The Twelve Kingdoms, Princess Joei takes up the role to usurp Youko's rightful place as the sucessor of her sister Joukaku.
 * As eventually revealed, Mashiro in Mai-Otome. Subverted given that she's allowed to remain on the throne anyway.

Comic Books

 * In the Sonic The Hedgehog comics, during the "Endgame" Story Arc, Dr. Robotnik replaced King Max with a robot double as part of his plan to finally defeat the Freedom Fighters.
 * In The Warlord, Deimos used an Identical Stranger to usurp Travis Morgan's position as Warlord of Skartaris.

Film

 * Many adaptations of The Man in the Iron Mask involve an inversion of this plot -- an evil king being replaced by his secret good twin.
 * Dave centers on an inversion of this plot: a bastard President goes into a coma and a look-alike is asked to stand in for him -- a look-alike who makes a much better president.
 * The novel and movie The Prisoner of Zenda, on which Dave was based, also uses an inversion, where the hero impersonates his identical cousin the King of Ruritania while the latter is imprisoned by The Evil Prince. He is a much better person and leader than the real king, who is dissolute and incompetent, but he ultimately helps restore the real king to the throne. (Although at several points he debates allowing the villains to kill the real king before foiling their schemes -- but mostly because he's in love with the king's fiancee.)
 * The Great Race takes time out from the actual race to send up The Prisoner of Zenda. The villain, Professor Fate, gets to be the one who looks just like the king-to-be.
 * The Great Mouse Detective has a fake queen -- and a relatively obvious one at that. Magnificent Bastard Ratigan forces a toymaker to create a robotic copy of the actual Mouse Queen, who -- standing in for the real deal -- will abdicate her throne in favor of Ratigan as the new king.
 * Later from Disney, Mickey, Donald, Goofy: The Three Musketeers saw Captain Pete of the royal guard pulling a similar stunt, substituting one of his own henchmen for Princess Minnie.
 * In Metropolis, the mad scientist Rotwang replaces leader-of-the-people Maria with a robot.

Literature
"''"Kings have reigned as true men in Valusia," the Pict whispered, "and yet, slain in battle, have died serpents—as died he who fell beneath the spear of Lion- fang on the red beaches when we of the isles harried the Seven Empires. And how can this be. Lord Kull? "These kings were born of women and lived as men! "Thus—the true kings died in secret—as you would have died tonight—and priests of the Serpent reigned in their stead, no man knowing.""
 * At least two Discworld stories involve this, or at least the idea of doing it. Apparently, Vetinari just has that effect on people.
 * There might be just one story where an actual Vetinari impersonation is an important plot point (The Truth), and one more (Making Money) where it happens as a more minor element. However, attempted coups of one kind or another have been the villain's goal so often in the series that Making Money hangs a lampshade on this trope by having an entire ward of a mental hospital populated by people suffering from Vetinari Delusion.
 * Terry Brooks' Magic Kingdom of Landover novel The Black Unicorn has this exact plot, but puts a fresh take on it by telling the story from the real king's point-of-view.
 * Robert E. Howard's Conan the Barbarian story "A Witch Shall Be Born" has Queen Taramis of Khauran replaced by her evil twin sister Salome. Salome treats the kingdom's farmers like slaves and excessively taxes city dwellers.
 * Older Than Print: There is an old Jewish legend about King Solomon capturing Asmodeus the Demon King. Eventually Asmodeus tricks Solomon into letting him out of the cell -- then impersonates Solomon and exiles him.
 * King Behind The Veil in Dreamlands by H.P. Lovecraft. You really need to read it, but in short: the proper king was decadent and has shown disrespect to gods and went to openly mock them. He returned, wearing veil forever. In reality he has been replaced by a race of beings, who enforced harsh but reasonably fair laws. The exiles from the society are secretly captured and used for their breeding program (which, Cthulhu Mythos being what it is, involves mosquito men and semi-sentient grubs).
 * That's just the role-playing game, and possibly some professional fanfiction. Lovecraft only implied that the King and his priests were inhuman, but never clarified just what they were, and if they had always been that way.
 * In L. Jagi Lamplighter's Prospero's Daughter trilogy, the legend of Solomon and Asmodeus is true. Solomon, near the end of it, took advantage of it to go to Hell and do a lot of damage to them, because they all took him for Asmodeus.
 * In Robert E. Howard's Kull story "The Shadow Kingdom", the Snakemen do this.

Live Action TV

 * The Doctor Who serial The King's Demons.
 * Sylar, the villain of Heroes, has attempted to Take Over the World by assuming the identity of the President of the United States. Twice!

Toys

 * Shows up in the Adventures arc of Bionicle where Makuta swaps places with Turaga Dume, ruler of Metru Nui in order to perform a crucial part of his Evil Plan.

Video Games

 * Breath of Fire II features a variation on this. Tapeta is the prince of Fort Nageur; unfortunately, he's shiftless, irresponsible and a hopeless romantic, and he's been abroad for quite some time (much of it spent transformed into an even bigger frog). By the time he comes back as part of Ryu's party, an impostor has taken his place: said impostor claims that Tapeta is impersonating him and has him arrested.
 * And the kicker? The people of Fort Nageur knew that Tapeta was the real deal; They Just Didnt Care on the grounds they were probably better off with the phony.
 * Chrono Trigger combines the Fake King concept with the Evil Chancellor to yield the Fake Chancellor.
 * Also subverted when the king starts acting like a dick. (More of a dick than usual, anyway). People do comment on his strange behavior... but it's the aforementioned trying to throw you off the trail.
 * The appropriately named False King in Demon's Souls
 * Disgaea 2 Cursed Memories gives us Overlord Zenon.
 * Dragon Quest loves this trope:
 * Dragon Quest III did it with the king of Samanao, who'd been replaced by a troll in disguise.
 * Dragon Quest V is another example, except that there isn't a Fake King, but a fake Queen Dowager. She pretends to be the mother of the current King of Coburg, and takes complete advantage over him, performing acts such as destroying The Hero's Doomed Hometown, recruiting monsters as soldiers, and executing anyone who defies her.
 * Dragon Quest VI pulls a reversal with a fake Demon Lord who turns out to be the king, as opposed to the fake king turning out to be a demon.
 * ...and then Dragon Quest VII did it with God. Yes, that God.
 * The Dragon Quest Monsters series did it more times than this troper can count. Probably because you can only battle monsters.
 * Again this trope turns up twice in Dragon Quest IX, the first with a moody girl in Bloomingvile  The second is with a vizier to the king
 * The first of The Elder Scrolls Games, Arena, begins in a prison where the player learns in a dream that the Emperor is an impostor, and must chase all over Tamriel for pieces of the Chaos Staff to defeat him.
 * Final Fantasy I had who was pretending to be a king so he could trick you into getting him the crown from the Marsh Cave.
 * In Final Fantasy II, we have a fake princess. Who eats rats. And demands sex from The Hero.
 * Final Fantasy IV, of course, is known for this one.
 * Jade Empire plays with this Trope a great deal.
 * The Legend of Zelda: The Minish Cap is one of the few that actually has the fake king as the final boss. On the other hand, the actual replacement of the king was a plot point for a change, too...
 * Oracle of Ages pulls a similar trick -- the sorceress Veran possesses the titular oracle, and goes back in time to manipulate the queen as an advisor (and later possess her, too). It results in a similar situation to the usual Fake King plot.
 * Twilight Princess has this with the Goron Leader, who has been possessed by a Fused Shadow. Not quite an example as the other Gorons were wise to the change the moment it happened and sealed him in the Goron Mines.
 * In Lunar: The Silver Star and its remakes, the leader of the floating city of Vane, Lemia Ausa, is replaced by Xenobia, a servant of the Magic Emperor. The real Lemia is imprisoned in the dungeon with a mask that blocks her memories.
 * In the first Might and Magic game, this is used. In the fifth game, the Big Bad takes the same identity, although not with taking over a throne.
 * Okami played with this with the leaders of Sei-an City; the game (and Issun) hint that Queen Himiko is behind the Emperor's illness and the city's curse, when in fact
 * Pokémon XD had six brothers impersonate the same person and the same time -- apparently unaware of the awkwardness of this situation.
 * Pokémon Gold and Silver/Crystal and their remakes (HeartGold/SoulSilver) also used this trope with Goldenrod Radio Tower's Director, being replaced by Team Rocket Executive Petrel in an attempt to get the Johto region to practically worship Team Rocket and Giovanni, it failed thanks to the player of course.
 * The plot of Prince of Persia 2: The Shadow and the Flame: once again, the Prince must Save the Princess from Big Bad Jaffar, who has magically disguised himself as the Prince.
 * Secret of Mana used it for the king of a republic.
 * Yaridovich in Super Mario RPG: Legend of the Seven Stars takes this trope to its logical extreme: He replaced everyone in Seaside Town, fooling exactly no one. Then he procedes to send Mario and Co. into a Fetch Quest to recover the Star Piece curently in possession of Jonathan Jones in the Sunken Ship and then he just waits for the MacGuffin Delivery Service to arrive.
 * It tried it again in Nimbus Land, where Valentina tried to pass off her giant raven henchman Dodo as the missing prince Mallow.
 * The Demon Lord Odin from Odin Sphere was subject to this in Gwendolyn's story. There is no direct comment that he had been acting strange, but the fact that Gwendolyn (his own daughter) was attacked by his guards stands as evidence enough.
 * The 7th Saga has an Excuse Plot largely involving this trope.
 * Not quite a king, but Sam & Max: Abe Lincoln Must Die! features a fake President who turns out to be a hypnosis device (a literal puppet ruler).
 * According to Babelfish translations of the one Japanese fansite of the Japan only Game Boy Color game that this troper could find, it's the explanation of.
 * In Shining of the Holy Ark the King is being possessed by an evil spirit for apparently no reason pertaining to the plot. Bonus points for ?the king is acting strangely? comments from the villagers and for removing the popular and good Sage/Advisor and replacing him with a scary, hated and clearly evil Witch/Advisor.
 * In Super Robot Wars Original Generation Saga: Endless Frontier, the heroes don't encounter a Fake King, but learn that a war between Formido Heim and Elfetale was cause by one of these. King Stahl of Formido Heim had discovered technology to travel to different dimensions, proceed to make use of it. Unforunately, the first world he visted was inhabited by the Einst, one of the Big Bads of the Super Robot Wars games. The Einst presumedly killed him and created an Evil Knockoff in its place. Said knockoff returned to the Endless Frontier and declared war in order to fulfill the Einst's goals. It wasn't until ten years into the war that leaders of the Orchestra Army, Formido Heim's main force, realized the true nature of their "king". The army rebelled and eliminated the fake, and sued for peace, while not telling the world why the war happened.
 * Happens in Romancing SaGa: Minstrel Song, and was working fairly well thanks to the leader in question's rampant Lawful Stupidness. While others comment on his strange behavior, only his daughter realizes that he's been replaced and recruits the heroes to help her; seems everyone else was just so used to him being a Jerkass with Moral Myopia that his declaring war on an ally just because he doesn't like the way she's protecting her Fatestone didn't seem too out of character...
 * Copy-X, Mega Man Zero's Big Bad Knight Templar, replacing Mega Man X as the ruler of Neo Arcadia. Notable that he was created for noble purposes (reflected in his creator), and he thinks that he's doing the right thing...
 * In Alundra 2, the Evil Chancellor Baron Diaz imprisons the king and has him replaced with a wooden manikin. Probably the only reason the population falls for this is because the only people other than the nobles in the resistance who actually see the 'king' work for Diaz.
 * Teikun Ō from Ace Attorney Investigations 2.

Web Comics

 * Parodied in Adventurers!: Karn meets a chancellor and immediately defenestrates him, on the Genre Savvy assumption that he's been replaced by a monster. It turns out that was the real chancellor; the monster assigned to replace him was out sick.

Western Animation

 * In an episode of DuckTales based on The Man in the Iron Mask, "The Duck in the Iron Mask".