Man in the Iron Mask

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

- Evil Overlord List item #3

So you've usurped your noble brother/half-brother's throne and your control is complete. Seems like the thing to do is to kill him and bury the corpse in a pauper's grave. But you're a nice Evil Overlord, so you opt simply to throw your brother, the one person who could cast your authority to rule your entire empire into doubt, into prison (or a monastery) and forget to tell anyone that he's your brother.

Of course, the hero discovers that the noble half-brother is still alive and frees him, restoring order to the kingdom, making the reader ask "Why Don't You Just Shoot Him?" before the hero shows up?

Sometimes this is justified on the grounds that shedding Royal Blood has side-effects, or that the land will suffer if the rightful king dies.

The essential criteria for this Plot trope:
 * Noble prisoner
 * The fact that you are keeping him or refusing to let him go is kept secret from the guards and/or the people at large
 * Releasing the prisoner would put the overlord's reign (or plans to reign) in jeopardy.

Comics

 * In Marvel's G.I. Joe comic, Crimson Guardsman Fred VII kills the original COBRA Commander and takes his place, concealing his own identity with the mask of CC's battle armour.
 * In The Warlord, Travis Morgan is captured and imprisoned by Deimos while an Identical Stranger usurps his position as Warlord of Skartaris. An iron mask is locked over Morgan's head to prevent his gaolers learning his true identity.

Film

 * The Man In the Iron Mask has had several adaptions. Richard Chamberlain starred in one where the older twin son had been spirited away, for leverage to make the younger one a puppet king, so the younger one was not, in fact, responsible. But he found out and ordered his brother imprisoned with the mask so no one could use it. The older one was rescued and managed to confuse the younger's flunkies so that his brother was sent off for the same fate.

The younger brother was afraid that their being twins meant there might be some connection, so that killing him would be dangerous.
 * Le Masque de fer (1962) is a French swashbuckling film. A lighthearted take on the novel, it stars Jean Marais as an old and hammy D'Artagnan.
 * The most recent film (1998) starring Leonardo DiCaprio as the king (Louis) and twin brother (Phillipe). Was notable for massive Adaptation Distillation: Louis being more evil than depicted in the novel, and . This was also DiCaprio's follow-up movie to Titanic during which legions of fangirls were still swarming to the earlier film in theaters: Iron Mask took second place.
 * In Asterix & Obelix Take On Caesar, Julius Caesar is locked in an iron mask and thrown into a dungeon by the traitorous Detritus.

Literature
"Thenceforward I am Taramis, and Taramis is a nameless prisoner in an unknown dungeon."
 * Subverted hard and fast in the Sword of Truth; part of the enchantments on the Rahl bloodline make that an unfortunate necessity. Any Rahl who isn't an absurdly powerful wizard is actually a "Pristinely Ungifted" whose propagation threatens the existence of the world. That's not to say that all Rahls kill their children so as to save the rest of their world. Richard runs into most of the survivors over his adventures, with various levels of emotional scarring and insanity, possibly deconstructing this trope by showing what those behind the iron masks would actually be like growing up in their father's country.
 * Rahl thinks he's this, but turns out to be delusional and possibly possessed.
 * Solzhenitsyn's The First Circle set in a Soviet-era "special prison" features a prisoner kept in isolation and referred to by the other prisoners as "the man in the iron mask", although his actual identity is generally known
 * In The Vicomte De Bragelonne by Alexandre Dumas père (Trope Namer), King Louis XIV has a twin brother who is kept in the Bastille—by their mother, the dowager queen—to avoid the possibility that he might usurp the throne. To make sure that the guards do not get the wrong idea, the man is placed in a secure part of the prison and forced to wear an iron mask to conceal his identity.
 * This is based on accounts of a real prisoner in the Bastille (among other prisons) forced to wear a mask. His identity was never revealed.
 * This also subverts expectations as
 * In some versions of Robin Hood, John claims to be raising money to free King Richard returning from The Crusades, but in reality is using the money to stay in power.
 * Played with a bit in The Prisoner of Zenda. You probably already know this, but:
 * Parodied in the Discworld novel The Truth, which involves a plot to dethrone Lord Vetinari by framing him for a crime using a man who looks just like him. After the plot is thwarted, William De Worde asks Lord Vetinari if he's giving his look-alike this treatment. Vetinari responds that the man is, in fact, alive and now employed by the Guild of Actors, appearing as Vetinari in stage productions and children's parties. William de Worde theorizes that he might occasionally be used as a stand-in for Lord Vetinari when the real one is unavailable for some boring task or posing for an oil painting, but Vetinari just answers that with a characteristic blank look.
 * On the other hand, for which of the two is being mistaken for the other more dangerous...? Rhetorical question, of course.
 * The Mage In The Iron Mask (Nobles series).
 * Includes a Lampshading of the fact that a Man in the Iron Mask would have to be let out of it once in a while to shave, or he'd suffocate on his own beard.
 * In Ursula K. Le Guin's A Wizard of Earthsea, Ged meets two people alone on a desert island, barely capable of understanding human speech. In The Tombs of Atuan Tenar explains that they were the last children of a royal line, and the God-Emperor was afraid to kill them, since they had Royal Blood, so he abandoned them there, very young. Subverted in that Ged did not rescue them; in fact, they were terrified at the prospect of leaving their island.
 * Notably, they were put to sea when they were children and were now at least middle aged. Royal blood clearly included excellent survival instincts, but they were a bit past their "crown by" date. The God-Emperor may have been cautious, but his grip on power was quiet definitely cemented when he had them exiled.
 * Eye Of The Dragon by Stephen King. In this case it's the Evil Chancellor who engineers the king's imprisonment by framing him with a very public trial, and when he's eventually freed the replacement king (his younger brother) is all too willing to give him back the throne.
 * Tsarmina's nice-guy brother in the Redwall book Mossflower.
 * One of the Xanth novels has the good King Omen imprisoned in secret by his usurper brother Oary. When foiled, Oary admits that he would have been more successful if he'd killed Omen, but he's not quite evil enough to kill his own brother.
 * In the backstory of the Ravenloft novel Tower of Doom, a nobleman's wife births a hunchbacked child and his undeformed twin. Their father doesn't lock up the malformed baby's face behind a mask, but he does lie about which kid was born first, raising the handsome younger twin as his successor while his blighted brother, the true heir, is confined to the titular bell tower.
 * In Robert E. Howard's Conan the Barbarian story "A Witch Shall Be Born", Salome, the Evil Twin, does this to Tamaris when becoming the Fake King. She wants to Break the Haughty on Tamaris.
 * In Robert E. Howard's Conan the Barbarian story "A Witch Shall Be Born", Salome, the Evil Twin, does this to Tamaris when becoming the Fake King. She wants to Break the Haughty on Tamaris.


 * Erik does this to Corwin at the end of the first book in Roger Zelazny's Book of Amber.
 * Somewhat subverted—it is later revealed that this was done as much to protect Corwin as to keep him off the throne.
 * King Jakoven in Patricia Briggs' Hurog series built the Assylum specifically to lock up his brother Kellen. Justified in that he was warned in a prophecy that it would be a very bad idea to kill his brother. While it's common knowledge that he's in there, most of the common people seem to have bought the idea that he's genuinely nuts, rather than unjustly imprisoned.
 * The Prisoner in the Mask by Dennis Wheatley.

Live Action Television

 * In one episode of Smallville, Lex is split into his good side and his evil side after accidentally creating Black Kryptonite. His evil side locks up his good side, complete with the requisite iron mask and Lampshading the situation.
 * In one alternate-universe in the Legend of the Seeker, Richard does this fairly stupidly, though in a rather unusual fashion. Unsurprisingly, it backfires. Turns out, leaving your omnipotence-macguffin out in the open, unstoppable though it may be, is a bad idea.

Tabletop RPG

 * In Eberron, the person (secretly a vampire) on Karrnath's throne is the great grandfather of the actual ruler, posing as his great grandson. It's strongly hinted that the real monarch is locked up in Eberron's equivalent of Alcatraz.
 * And with an actual iron mask, no less.
 * As the Dungeons & Dragons world operates under Death Is a Slap on The Wrist, it's preferable to keep foes with high level resources imprisoned instead of killing them because more powerful resurrection methods work without a body, allowing the recently deceased to pop up in friendly territory as soon as someone forks over the stuff to revive him.

Toys

 * In the second Bionicle movie,  gets this treatment, down to the mask. Weird but funny in hindsight, because most characters wear masks anyway. The character in question actually complied with the treatment to be able to train three of the Toa Metru.
 * Mata Nui by Makuta, though that one turns out to be significantly more complicated.
 * The real, by Makuta.
 * The Toa Hordika could be considered a version of this, though Roodaka tried to execute them by pushing them off a skyscraper.

Video Games

 * In Arcanum: Of Steamworks and Magick Obscura, while on prison island, the player can stumble upon an old man, who turns out to be thought-to-be-dead rightful king of kingdom of Cumbria. Inevitably, player can help him regain the throne, and inevitably, under his command the kingdom thrives. This is, however, due to his willingness to commence reforms and accept technology (which, by the way, was the reason why he was couped out of power by his technology hating brother), not some kind of magical property of Royal Blood.
 * Appears in Lunar: The Silver Star.
 * A subversion of this appears in the Kingdom Hearts series, with the character  in reality   his kingdom and his very name are taken by   of Kingdom Hearts I and II separately.
 * Because he's technically noble (a knight), Final Fantasy XIIs Basch fon Ronsenberg (of Dalmasca') counts. His twin brother put him in prison after he (the twin) framed Basch for the murder of the king of Dalmasca years earlier. The public at large assumed him dead, though instead he's in chains at the bottom of the world's most infamous prison-fortress. He goes on to be freed by Vaan, Balthier, and Fran, eventually joining them permanently in order to safeguard Princess Ashe.

Western Animation

 * Disney's DuckTales has "The Duck In The Iron Mask". Scrooge visits his old friend Count Roy, who rules a small kingdom, to find that his twin brother Ray has usurped the throne. Roy, in the obvious role, explains that he never told Scrooge about his brother because he felt responsible for his brother's disappearance.

Real Life

 * The legend of the Man in the Iron Mask was based on actual records found from Bastille. There are a lot of theories regarding the Man's identity, but very little information remains of the real events.
 * What has been discovered is that the Iron Mask itself was an exaggeration - the mask was just silk, and the Man probably wore it voluntarily.
 * A fair amount of evidence points to his having been an insignificant figure whose knowledge was dangerous, not he himself. You will not find that in any of the legends.
 * Aversion: The Ottoman Sultan Mehmet the II (the guy who took Constantinopol) realized that having siblings around to challenge the throne was not a good thing for the ruler and the kingdom so he not only recommended fratricide, he legalized it (on a royal level) and put together a framework to deal with troublesome siblings. It was only removed during the later periods of the empire and overall, it is generally considered a success.