When you have access to Time Travel, you always risk running into yourself. In some universes this can lead to a lot of problems, but in others the rules are a bit more relaxed. This doesn't mean there aren't any problems though. People change over time, you included, so who's to say that you and yourself would be friends? Who's to say you'd even like each other? Who's to say one of you wouldn't kill the other?
That's where this trope takes effect, when someone murders their past or future self. This could be to spare them from a terrible future, or maybe to stop you post Face–Heel Turn. Or maybe simply because I Hate Past Me.
Sister trope to Killing Your Alternate Self. This action may result in a Stable Time Loop if the past kills the future, or a Temporal Paradox if the future kills the past. Not to be confused with Grandfather Paradox, where one kills their ancestor, ending their own existence.
As this is a Death Trope, unmarked spoilers abound. Beware.
- In Extermination, Cable is killed by his own past self for his failure to properly protect the timeline by not immediately returning the time-displaced original X-Men to their proper time. The younger version of Cable then takes over as the main version of Cable appearing in the comics.
- Wonder Woman: Odyssey when the Nemesis possessed Wonder Woman can't get her younger temporal duplicate to join her she tries killing her, which she intends to have result in her own death. The uncorrupted Wondy uses Nemesis's attempt to weave the threads of fate that separated her into two back together thereby restoring the timeline and preventing Nemesis from possessing her in the first place.
- Astral Displacement: Sapphire believes the only way to evade White Sapphire's future vision is by destroying her own past self, thus she'll become a temporal anomaly and can act undetected. Aquamarine, knowing how stupid and dangerous this idea is, takes Sapphire back to the present and talks her out of it.
- The Doctor Who/Smallville crossover The Clinton Street Car Crash concludes with Chloe Sullivan causing the titular crash to kill her own past self; through a complex temporal paradox, the General Zod of Superman's era created the Smallville timeline by saving Chloe from a childhood accident to start a chain of events that would lead to Lex Luthor arriving in Smallville during Clark's childhood and thus essentially retard Clark's growth into Superman. Chloe's sacrifice to cause that same car crash kills her own past self, but also restores the original timeline with Clark as Superman, as Lionel was now never able to find someone to run the Luthorcorp plant in Smallville and thus had no reason to send Lex there.
- The Friends fic The One Where Heckles Has An Existential Crisis is based around the idea that Mr Heckles, the group's downstairs neighbour, is actually a version of Chandler who never got over his commitment issues and ended up driving the others away after his fear of long-term relationships drove Monica to break up with him. When Heckles finds himself in the past, although he never reveals his true identity to the group, he chooses to kill himself after altering his belongings just enough to hide his identity while affirming what he was like as a person, in the hope that seeing these assorted relics will inspire his younger self to overcome his own fears and commit to Monica.
- Minions: The scientist Professor Flux invented a time machine and brings back copies of himself from the future to help in his lab until the original Flux is accidentally killed, causing all the duplicates to be erased from existence.
- Avengers: Endgame: The unfortunate fate of 2014 Nebula. Because of an unexpected side effect of the Avengers time traveling really screws with Nebula's cybernetic enhancements (of which she is almost completely composed of), 2014 Nebula starts receiving the recorded memories of her present day self, up to when the team uncovers the locations of every Infinity Stone throughout the years. When 2014 Thanos watches the memories played back before him, he immediately sets out to capture present day Nebula and sends her 2014 self in her present self's place. Lacking her present self's character development and any bond she eventually would have had with 2014 Gamora (who herself was growing ever more horrified by Thanos' actions and already planning on defecting), 2014 Nebula enthusiastically embraced her mission, very nearly costing the Avengers a second, much worse defeat when she successfully brought 2014 Thanos and his forces into the present day and tricked Hawkeye into giving her the complete Infinity Gauntlet. She does end up cornered by her present day self and 2014 Gamora, the latter of which tries to reason with her and get her to abandon Thanos for good. Sadly, the present day Nebula shoots her 2014 self before she could even have the chance, knowing full well how desperate her 2014 self was to please Thanos, how terrified she was of him then, and knowing that they can't risk Thanos winning again.
- In the ending of the director's cut version of The Butterfly Effect, the main character Evan uses his Mental Time Travel powers to go all the way back to when he was a fetus still in his mother's womb and strangles himself to death with his own umbilical cord so that he couldn't ruin the lives of everyone he would've met. It's also strongly implied Evan's two unborn siblings who were stillborn had the same powers and went through the same thing.
- In the 2012 film Looper, criminal syndicates send assassination targets back in time for past assassins, called loopers, to kill. However, if a Looper lives to the point of Time Travel's invention, then they are sent back in time to be killed by themselves, "closing the loop". At the end of the film, young Joe kills himself in order to stop old Joe's rampage.
- In Triangle, the main character is stuck in a time-loop that keep sending her to different places in the movie's timeline, dealing with a version of her murdering all the others. This means that in one timeline, she's the one murdering her past and/or future selves, while in every other timeline, she has to try and stop the killing.
- In the final Artemis Fowl book, "The Last Guardian", two different versions of Opal Koboi exist as a result of a past version of Opal bringing herself forward in time in a previous book, "The Time Paradox". The present version of Opal tricks the past version and arranges for her assassination, and past Opal's death causes a Temporal Paradox that the surviving Opal manipulates to transform herself into a super-being with incredible magical powers.
- In the Eighth Doctor Adventures novel Alien Bodies, a Faction Paradox agent, Cousin Sanjira, is punished for letting the Relic slip through his fingers by being forced to murder himself as an eight year old, causing his whole timeline to unravel into a state of perfect paradox.
- Harry Potter And The Prisonerof Azkaban: While using the Time Turner, Hermione has to keep Harry from meddling with their past events, explaining that some time-traveling wizards have even killed/been killed by their past or future selves.
- In the first book of The Licanius Trilogy, Caedan sees Davian come back and give him a "The Reason You Suck" Speech. Caedan kills Davian, but this speech nevertheless sparks a Heel Realization. Near the end of the third book, Caedan and Davian have become friends, and Caedan begs El for the chance to take Davian's fated death on himself. It's at that point that he realizes that since he technically killed Davian as a baby (in a way that the latter was able to come back from), he can take Davian's shape (shapeshifters in this setting can only take the shapes of those they have personally killed), go back in time in his place, deliver the speech that will start his redemption, and die at the hands of his own past self.
- The Truth has Mr. Tulip, after his demise, being shown all the horrible things he did to others during his life. When Death explains that he may reincarnate before his previous life was born, an utterly broken Mr. Tulip expresses a desire to hunt himself down and kill himself. Death has to explain that reincarnations don't usually remember their previous lives.
- In the Andromeda episode "The Unconquerable Man", a future version of Dylan Hunt's treacherous first officer Gaheris Rhade — having come to regret this role in overthrowing the Commonwealth, and learned that Dylan, not he, is the right person to restore it — travels back in time, kills his younger self and takes his place. He then throws the fight with Dylan which he originally won, thus allowing the events of the series to date to occur.
- Doctor Who: "The Doctor Falls" finds both the Harold Saxon Master and his future self Missy working with the Doctor to fight off an army of Cybermen. After they find a way to flee, the Doctor tries to convince them to stay and help save the civilians. They refuse, but as they're about to leave, Missy kills Saxon, beginning his regeneration into her (as far as she knows). Disgusted by the fact that any version of himself would stand with the Doctor just to save a bunch of humans, he kills her with a full blast shot from his laser screwdriver, making her incapable of regeneration.
The Master: You see, Missy, this is where we've always been going. This is our perfect ending. We shoot ourselves in the back!
- In The Flash (2014), speedsters are able to create duplicates of themselves by traveling slightly back in time. The first character to actively utilize them, Zoom, was well known for killing his own Time Remnants, killing both that appeared on screen.
Zoom: Believe me, getting my Time Remnant to agree to me murdering him took a bit of convincing. But once he saw the, well the genius in my plan, he was all for it.
- The King: Eternal Monarch: When Lee Gon and Lee Lim travel back to the day of the palace coup, Lee Lim goes to his younger self to warn him to revise the plan. His younger self rejects the advice and kills him to take his flute-half for himself, only for it to vanish. The Lee Lim from this timeline, however, doesn't meet this fate, so he's still around advancing his plans when Lee Gon returns to the present.
- The Outer Limits (1995): The episode "Tribunal" features a Nazi Grandpa who is punished by being sent back in time to the concentration camp he used to work at, dressed as an inmate. He tries to convince his younger self that they are the same person but is simply shot in the head instead.
- In the Red Dwarf episode "Tikka to Ride", the Starbug crew travel back in time and unwittingly prevent the JFK assassination. They find out that as a result, Kennedy's womanizing is revealed and he's impeached and disgraced; furthermore, J Edgar Hoover is blackmailed into letting the Soviet Union re-install nuclear missiles in Cuba, so most major US cities are evacuated. The group go to 1967 and encounter Kennedy as he's about to be transferred to a prison, and give him the chance to fix the timeline by taking him back to 1963 to shoot his past self from the grassy knoll. This fixes the timeline, and Kennedy thanks the crew for letting him save his legacy before he fades away.
- The Star Trek: The Next Generation episode "Time Squared" involves Picard meeting his past double and killing him with a phaser set to "kill" to keep the timeline smooth.
- Mage: The Awakening: The highest-ranked Doomsday Clock Apocalypse Cultists are required to reach back in time and kill their past selves, allegedly freeing themselves from the "prison" of time and causality. In fact, the act lets an Abyssal entity devour their existence and take their place.
- In Warhammer 40,000, the Waaagh! of Warlord Gritgutz was thrown into disarray after it traveled back in time, and the Warlord decided to kill his past self to have a spare of his favorite gun.
- In Bioshock Infinite, Booker Dewitt and Father Comstock are the same man, the only thing separating them is a decision. After the battle of Wounded Knee Booker refused his baptism while Comstock went through with it. Near the end of the game Booker drowns Comstock on his airship before allowing himself to be drowned moments later to kill Comstock in other timelines where he exists.
- Optional and Played for Laughs in Escape from Monkey Island. In the Mists of Tyme Swamp, Guybrush encounters his future self who gives him a few items, including a gun. The player can then use the gun to kill the future Guybrush, but this results in time resetting itself.
- In the Legacy of Kain series, Kain raises several Sarafan vampire hunters from the dead and transforms them into vampires so that they can serve him as lieutenants. One of these vampires, Raziel, eventually travels into the past and comes into conflict with the Sarafan Order when he learns that they were a lot less noble than they'd like people to believe, and ends up slaying several of the Sarafan's prominent members, including the hunters whose corpses he and his brothers will one day be raised from.
- Prince of Persia: Warrior Within: A Necessary Fail is needed for the one using the Mask of the Sand Wraith to change the past. The Maharajah learned this when he saw a Sand Wraith, actually his future self, get killed while saving his past self from an assailant, and realized he had to step back and allow his past self to be killed when the time came. From the Maharajah's writing, the Prince remembers when the Sand Wraith was killed by the Dahaka while confronting him, and decides to avoid the confrontation to let the Dahaka kill his past self instead.
- Rohen Tahir from Spellforce is trapped in a Stable Time Loop in which his younger self travels forward in time, unknowingly murders his older self, and becomes the Big Bad of the game, while his older self does a Heel–Face Turn and travels back in time to right the wrongs his younger self caused, becoming the Big Good and setting in motion the events that lead to his murder.
- Doing this as a Temporal Warden in Tales of Maj'Eyal unlocks the Paradox Mage class.
- Total War: Warhammer III: In Kairos Fateweaver's quest battle for The Staff of Tomorrow, the battle is between his past and future selves and armies. Quite fitting, since Kairos' two heads can each only see the past and future.
- Fate/stay night: This is the primary goal of Archer, aka Shirou Emiya, who seeks to kill his past self in order to wipe himself from existence and free himself from the shackles of the Holy Grail War. He also wants to do it to spare Shirou from going through the same experience as he did, trying to become a hero of Fuyuki City and ultimately becoming a Fallen Hero. Unfortunately for him, no matter how laid out his plans are, several other factors prevent Archer from achieving his goal at the worst possible moments.
- Bonus Stage ends this way, due to a Creator Breakdown: Phil steals a time machine and goes back to the first episode, where he kills his past self and his costar, Joel, and then hangs himself, causing the entire show to be removed from existence (and the hosting website).
- In the Eddsworld episode "WTFuture", Edd gets a visit from his future self, who reveals to have traveled to the past with the intent on killing his past self to spare himself of living in a future where cola is outlawed as a drug.
- A close variant in one of Star Trek Online's story blogs. In "Army of Me", Istra, a Starfleet temporal agent, is ordered to arrest her own future self to correct a temporal anomaly.
- SCP-4264 from the SCP Foundation focuses on a teacher that could warp reality according to the example questions used in his lessons. When this leads to his students getting killed by a government agency responding to the anomaly, he reverses his actions by sending himself back in time and exploding upon arrival so he and his past self perish before the trouble starts.
- In the Family Guy episode "Stu & Stewie's Excellent Adventure", Stewie travels forward in time to meet his older self and is horrified to discover he grows up to be a loser, working a dead-end retail job, living in a run-down bachelor pad and spending most of his adult life as a virgin. When he discovers all his problems can be traced back to a traumatic near-death experience, he travels into his own past and succeeds in saving his past self from the incident... only for his past self to disintegrate his future self with a laser pistol.