Kill and Replace

""Fear not. Your life will not go unlived.""

- Dimir Doppelganger, Magic the Gathering

""I have copied all that is you. You are no longer necessary.""

- Dark Bowser, Mario & Luigi: Bowser's Inside Story

A Doppelganger, Shape Shifter (in a speculative fiction setting) or an identical twin for more mundane stories seeks to kill the original and take their place. If they're quick and quiet, nobody will suspect a thing until it's too late.

If the murderer is a full-on Shape Shifter, this technique may will be employed iteratively to pierce increasing layers of security. Just kill and replace the hapless guard, then the sergeant, then his lieutenant superior...

Tends to be caused by the Cloning Blues. Fantasy cousin of Twinmaker.

Compare Dead Person Impersonation. Compare Mugged for Disguise and Dressing as the Enemy, where the victim at least gets to live, albeit knocked out and half-naked.

Anime & Manga

 * In Escaflowne, a shape-shifter does this to a hypnotist in order to infiltrate a prison and extract information from the prisoners.
 * In The Law of Ueki,
 * In Angel Sanctuary
 * The Akuma from D.Gray-man do this when they kill the person who called them back to life and take their form.
 * An episode of Boogiepop Phantom has two cops discussing an urban legend about a being called Manticore. At the end, Cop A wonders, just how did Cop B know so much about the Manticore? Cop B shows him.

Comic Books

 * In Excalibur, Courtney Ross was murdered and replaced by her other-dimensional double Sat-Yr-9.
 * Also in the Marvel Universe, the female Dire Wraiths [enemies of ROM Spaceknight and fuglier version of Skrulls] did this, helped by using their drill-like tongues to eat the victim's brains and gain their memories.
 * Jane Doe in the Batman universe is an insane serial killer who has this as her MO - she kills people and wears their skins, honestly believing herself to be that person, until she is either found out or breaks out of the identity to find another victim.
 * In the Adam Strange: Planet Heist miniseries a Durlan kills Doc of the Omega Men and takes his place, waiting for the right time to strike.
 * Gold Digger (series): The Gaoblin are an interstellar race who have killed and replaced four entire species: the trolls, the elves, the Atlanteans, and the Kryn. The "new" versions did such a thorough job, and continued the originals' culture so well, that the change had been lost to history for millennia.

Film

 * The T-1000 does this several times in Terminator 2, it being his standard M.O. to kill a victim and copy their appearance/voice: John Connor's foster mother, a security guard in the insane asylum where Sarah Connor was being held and, very nearly, Sarah herself . Also used partially in the first film, where the T-800 kills and impersonates the voice of a cop as well as Sarah's mom.
 * Futureworld, the sequel to Westworld. Clones are programmed with the knowledge of their original and ordered to kill them and take their places.
 * Mystique does this several times (most notably to Henry Gyrich and ) in the X-Men films.
 * The titular characters in Invasion of the Body Snatchers do this.
 * The title creature in The Thing is a cross between Kill and Replace and Puppeteer Parasite. It infects a host, slowly replacing them from the inside out until none of the original remains becoming just the form of a new "colony" of Thing cells.
 * The Bug does this to Edgar in Men in Black by skinning him and donning his "nice new Edgar suit".
 * In The Last Starfighter, an alien Zandozan assassin does this to a local law enforcement officer in order to blend in with the human population.
 * In the movie Krull
 * In the box office flop Impostor, Gary Sinise's character is accused of being an alien biorobot who has killed and replaced the scientist. They plan to prove themselves right by cutting him open to look for a biological bomb. He escapes and spends the rest of the movie trying to prove them wrong..
 * For bonus points, he is being chased by Bobby Goren.
 * In G.I. Joe: The Rise of Cobra, Cobra Commander plans to have Master of Disguise Zartan murder the president and take his place.
 * This forms part of Moriarty's plan in Sherlock Holmes: A Game of Shadows.

Literature

 * A Ray Bradbury story, "Marionettes, Inc.", where a man buys a robot double to please his wife so he has more time to have fun. Eventually when he tries to put the robot back in the box after realizing the robot has fallen in love with his wife, the robot puts him in the box where he presumably dies.
 * The Sweet Valley High book The Evil Twin was about a psychotic woman, Margo, who happened to look just like the Wakefield twins. She planned to kill Elizabeth and take her place. Then, in Return of the Evil Twin, Margo turned out to have a twin, Nora, also psychotic. This time Margo and Nora planned to take over the lives of both twins, but their plans went awry when they argued over who got to become Jessica.
 * The alien invader in John W. Campbell's short story "Who Goes There", which was the inspiration for The Thing movies.
 * The Doctor Who Eighth Doctor Adventures contain a kind of inversion, where the copy is killed in order to have them replace the dead original. Sort of. So... Also done with a whole different twist:
 * Dune had Bene Tleilax Face Dancers, shape-shifters who absorbed victims memories and physical identity then killed them. This is far from being the creepiest aspect of the Bene Tleilax.
 * There is also the side effect of Face Dancers Becoming the Mask if they spend too much time pretending to be the same people.
 * A 'kidnap and replace' variant of this appears in the German SF novel Der Verbannte von Asyth, whose plot revolves largely around aliens replacing important individuals on Earth with masked infiltrators of their own kind. The originals are kept alive at the aliens' hidden base and thus remain conveniently available for questioning.
 * Subverted in a surprisingly cruel fashion in Good Night, Mr. James, which even the author admitted was a little vicious.
 * In HPLovecrafts The Case of Charles Dexter Ward the main character Charles Dexter Ward uses arcane knowledge left by his infamous identical great-great-grandfather to revive him who procedes to Kill and Replace him. The identical grandfather is lampshaded in the story with mentions of the how uncanny their resemblance.
 * In a short story by Paul Jennings, the narrator tells of his troubles with a duplicate that had all his memories and kept trying to take over his life because it thought it was him, so that in the end he had to kill it in self-defence. The end of the story implies that it's the narrator who was the duplicate.
 * Horza, the main character in Iain M Banks' Consider Phlebas is a member of a human subspecies called Changers, who have biological faculties that allow them to take on the appearance of other humanoids (although it takes a lot of concentration and food to complete a change). Horza in particular has been trained as a spy, so he also keenly observes his targets so that when he kills and replaces them he copies not only their appearance but their personality and mannerisms.
 * In Harry Potter and The Deathly Hallows,.
 * The Polyjuice potion is a less heinous form of this. It's used to replace someone, but whoever you're impersonating has to be alive when you take their hair or other part, so you have to keep them alive if you want to look like them for more than an hour. In practice, it's Capture And Replace.
 * Kandra do this in Mistborn, though in an odd variation, they are bound by Thou Shall Not Kill -- their employers must provide the corpse. Whether or not they participate in the Cold-Blooded Torture that generally goes on first (in order to root out any secrets necessary to make the impersonation successful) isn't mentioned.
 * "The Hanging Stranger" by Philip K. Dick featured a man who had been working in his basement for days emerging and heading into town, only to spot a body hanging by a noose from a lamppost in the middle of the town square. He starts freaking out, mainly because nobody else seems to notice or care. It quickly becomes apparent that something has infected or replaced almost everyone else in town as the opening of a secret invasion. The guy eludes a manhunt, desperately trying to get to the next town over to warn them before it's too late. The story ends as he is being debriefed by the police of the neighboring town about his story. Just as it dawns on him that the corpse in the town square must have been a trap to get people like him (those missed for whatever reason during the wave of Kill and Replace) to out themselves by their reactions, one of the policemen walks in with a noose all ready for him...
 * In Sergey Lukyanenko's Autumn Visits, six people find themselves face-to-face with the Envoys, who look just like them. Five of them (Kindness, Knowledge, Art, Strength, and Growth) cooperate with the originals, while the Envoy of Power simply shoots the politician he is duplicating with his own gun and takes his place. When later asked why, he simply replies that, while the other Forces only grow stronger with numbers, Power must be concentrated and never shared.
 * To note, Power's previous incarnations include Napoleon Bonaparte and Joseph Stalin, who also did not like to share.
 * One of the many, many Epileptic Trees regarding The Final Problem states that Moriarty killed Holmes at Reichenbach Falls and then took his place. How did Watson not pick up on this? The same reason Valley of Fear doesn't quite gel with previous accounts: Moriarty totally befuddled his wits. And where did all the subsequent short stories come from? Well, it turns out that Holmes' usual schtick was actually a pretty appealing way for Moriarty to use all that brainpower. Just ever-so-slightly more evil about it. (Sad part? There are a lot of Holmesian scholars crazier than this.)
 * Bimbos of the Death Sun has a Red Herring scene where someone starts screaming bloody murder; it turns out to be a game of Dungeons and Dragons where one player murdered another just before his wedding and used a shapeshifting amulet to take his place.
 * In Empire From the Ashes, Dahak destroyed our original Moon and took its place.
 * Wild Cards. Third generation swarmlings could kill people and change their own shape to take their place.

Live-Action TV

 * In Heroes, Sylar the super serial killer is also doing this now that he's a shapeshifter. There's also an incredibly messed-up inversion of this trope:.
 * James Martin (the shapeshifter Sylar stole his power from) played it straight and inverted it. He killed and replaced one of Danko's soldiers, then when he impersonated Sylar,
 * This was the Autons' plan in the classic Doctor Who serial "Spearhead from Space": creating plastic duplicates of prominent public figures in order to replace them.
 * The Slitheen do this in the 2005 revival, adapting their victims' skin into suits which they use to masquerade in their place.
 * Attempted by Faith in Buffy the Vampire Slayer in the season 4 episode This Year's Girl - using a device from the Mayor, she
 * Pulled off for the bulk of the second season of Alias, beginning with  Used again without the 'kill' part in season 5, when
 * Hawaii Five-O episode "Labyrinth". As part of a kidnap plot, a woman has plastic surgery to look like a wealthy socialite. She then murders and disposes of the victim and tries to take her place.
 * The Worm creatures in Kamen Rider Kabuto do this. They also take their victims' memories and can use them to Shapeshifter Guilt Trip their enemies. Note that they occasionally do the "replace" before they're done with the killing, as seen in one episode where a Worm victim manages to survive and the heroes have to Spot the Impostor.
 * In Fringe, is murdered offscreen by a shapeshifter, who proceeds to impersonate him for several episodes.
 * Not to mention at least a dozen other side characters.
 * Terminator: The Sarah Connor Chronicles:
 * Several individuals relevant to the timeline are murdered by T-888 infiltrator models whose outer flesh Skynet can shape into perfect copies of anyone in the 21st century.
 * Cromartie loses his initial outer flesh and uses plastic surgery to impersonate & kill George Lazlo.
 * The T-1001 model is a slightly more advanced "liquid metal" version who.
 * Cameron's original purpose was to impersonate a future resistance fighter named Allison. Though not outright stated, it is implied that Allison was an intimate of John Connor, and Cameron's purpose was to get close to him and assassinate him. Affter questioning Allison about her past, Cameron breaks her neck.
 * Used by a Loony Fan of London Tipton in The Suite Life On Deck, although here it's more like "Lock In A Closet And Replace".
 * A similar incident happened in Big Time Rush.
 * Lost plays this a little differently with  who cannot kill any of the Candidates himself creating a plan that will result in  's death at the hands (literally) of   and allow   to take on his form.
 * A favoured tactic of the Mysterons in Captain Scarlet.
 * The Big Bad of the Russian series Dossier On Detective Dubrovsky employs this tactic boosted Up to Eleven. With the help of a brilliant plastic surgeon he gradually has all the deputies of the State Duma kidnapped, murdered and then replaced with identical twins made from his minions.
 * On Monk, a man has an affair with a woman who is a dead ringer for his wife. He plans a trip with the wife; the mistress/lookalike kills the wife at the airport and the husband dumps the body. She then takes the wife's seat on the plane, essentially giving them an 'alibi' by making it seem like he and the wife were on the plane together.
 * One episode of Law and Order had a woman on trial for killing her sister; it was revealed midway throughout the trial that she was, in fact, the 'dead' sister, having switched identities with her to avoid some mobsters.
 * CSI episode "Pirates of the Third Reich":
 * The Outer Limits
 * 1960's episode "The Hundred Days of the Dragon". An Asian government kills a U.S. Presidential candidate and replaces him with an imposter whose face has been molded to match the candidate's by use of a chemical.
 * An episode of the 1990's revival had a talk show host interview a man who claimed to know of a conspiracy which replaced prominent figures with clones loyal to the creators. At the end of the episode, the "conspiracy nut" is killed, at which point the shocked host sees a duplicate of himself wearing the same clothes. The final scene is a report by the clone who dismisses the claims of the "nut" who has "killed himself".
 * In season 7 of Supernatural, the favored tactic of the Leviathan.

Newspaper Comics

 * Used as an innovative sales technique in Dilbert.

Tabletop Games

 * Dungeons and Dragons
 * This happens in any adventure in which a doppelganger monster appears, because killing people and replacing them is their modus operandi.
 * Also used by Sivak draconians in the Dragonlance setting.
 * Mystara Monstrous Compendium Appendix supplement. A Randara chooses a human victim that has the respect of and power over other humans. It uses ESP to read the victim's mind, then kills and eats the victim. It then takes the victim's shape and takes their place in society, using their victim's prestige to obtain more human prey.
 * 3rd Edition Creature Collection. The Skin Devil kills a victim, removes a two inch square patch of skin and uses it to grow an outer skin to match the victim's.
 * The Chill adventure Veil of Flesh had the Ganabe monster, which gains power by murdering human beings and takes the form of its latest victim. The monsters in the adventure took the form of Secret Service agents and police officers in a plot to assume the form of the leaders of France, Great Britain, the Soviet Union and the U.S.
 * Exalted: The Lunars have the ability to become any creature by ritualistically stalking it, killing it, and drinking its heart's blood. This same quality applies to humans, but only that particular human. Lunars do have access to shapeshifting Knacks, however, that allow them to refine the process, such as assuming the person's fate as well as their appearance, allowing them to change their clothing and hairstyle as they wish, and even being able to turn into the person temporarily by just taking a small sip of their blood (or, at higher levels, just by having sex with them).
 * Call of Cthulhu features a spell that allows its caster to take on the semblance of a recently deceased person...by ritually consuming the corpse over the course of several days.
 * Starblazer Adventures, based on the 1980's British science fiction comic. The sample adventure in the main rules, "The Shapechangers of Charon", is about a single Shapechanger who kills and takes the place of a number of characters aboard the starship HMS Traveller.

Videogames

 * Treskton in The Nameless Mod is a being created through the countless misspellings and mispronunciations of Trestkon's name seeks to kill Trestkon and take his place.
 * In Soul Calibur 3 you can fight shadows as bonus fights (and one mandatory one in Zasalamel's story), as they damage the player, the player slowly becomes shadowed themselves while the doppelganger becomes more and more real.
 * This is part of one of Gomez's conspiracy theories in Vampire Bloodlines (read it here).
 * the Duplighost in Chapter 4 of Paper Mario: The Thousand-Year Door, after being (supposedly) defeated by Mario, takes Mario's appearance and name and tries to erase Mario himself.
 * The final stages of the original Baldur's Gate were beset by doppelgangers who killed prominent people in and around Baldur's Gate and assumed their identities to support the Iron Throne.
 * Prototype. You approach your target (an officer or some other guy with what you need) and tear him apart while extracting not only his appearance (including clothes) but also his memories. And there is a stealth version, where you kill your victim and step forwards into their disintegrating body. If no military personnel see you in the exact moment, they won't even notice the change. Makes stealth missions quite easy, and with a bit of patience you can wipe out an entire military base this way without ever raising the alarm. All that's left is a pile of discarded weapons.
 * Also,
 * The Snatchers from Snatcher has this as their primary MO.
 * Traffic Department 2192 has a heroic version. The primary antagonist faction are Alien Invaders who've wiped out countless societies.
 * In Mass Effect 2,.
 * Also, in the Lair of the Shadow Broker,.
 * The same thing happened.
 * In Team Fortress 2, it's possible when playing as a Spy to kill the player you are disguised as. In fact, you even get an achievement for it! His new knife, "Your Eternal Reward" silently kills the enemy, phases their corpse out of existence, and disguises him as the victim instantaneously. Keep a close eye on that Medic of yours.
 * Even sneakier, it also doesn't give normal kill notifications and spoofs various other effects.
 * Strangely inverted with the Spy watch, the "Dead Ringer". You can't see when an enemy Spy pulls it out, but when he does, and you shoot him, the Spy instantly "dies", turning invisible and leaving behind a fake corpse (with a fake kill notification!). This leaves the Spy free to escape from a bad situation or go assassinate another target.
 * Happens accidentally in Phoenix Wright: Justice For All. In the second case,
 * The Foxhound Unit is known to utilize this tactic, most notably when Ocelot "accidentally" kills  then has Decoy Octopus impersonate the dead man.
 * This is the whole modus operandi for the Metroid series' X Parasites, and there's a very real threat of them doing so on a galactic scale.
 * The original Mechwarrior 2 had players do this as part of one of the campaigns. Piloting an identical 'Mech, the player had to kill the enemy patrol 'Mech and take its place to get near to the actual target, the facility it was guarding, without blowing their cover (which happened to many, many trigger-happy players).
 * Ninetails in Okami murders a priestess and takes her place. The priestess' ghost eventually finds the heroine Amaterasu and reveals the truth, though not before Ninetails murders another heroine who is attempting to discover Ninetails' stronghold.
 * In Final Fantasy IV this was done to the king of Baron before the events of the game start (although naturally the game never used the word "kill").

Western Animation

 * "YOU DOODLE! ME SPONGEBOB!"
 * An episode of The Real Ghostbusters has ghosts that take the form of the original Ghostbusters, in their original uniforms none the less, trying to kill them.
 * In the Batman: The Animated Series two part episode "Heart of Steel," the evil computer HARDAC decided that humans were too dangerous due to their imperfections and began replacing them. While it was planning on killing its victims once it had extracted all the information it could, they are ultimately rescued before it can do so.
 * A follow-up episode featured HARDAC's final creation, a robotic duplicate of Bruce Wayne/Batman activating long after it's initial defeat. The duplicate lacked a complete memory file, and thus believed itself to be the REAL Batman until it learned otherwise. It then began trying to carry on HARDAC's mission by eliminating Batman and replacing him. Turns out, HARDAC did TOO GOOD A JOB copying Bruce Wayne's mind, and the robotic duplicate can't handle the guilt of thinking it actually killed a human being (Batman was actually ok though) and self-terminated).
 * In Young Justice, this is said to be the standard procedure of Project Cadmus.

Real Life

 * Slavemaking ants follow a gory form of brood parasitism: the queen sneaks into the hive of an ant colony, kills off the original queen and takes on her pheromones, fooling the colony's current ant crop into becoming her servants, raising and feeding the queen's offspring.