->''"Somewhere in [[TheMultiverse the multiverse]], there is a world I call '[[TropeNamers Earth Prime]]'. Every Earth is a variation of this one, the original--and once I destroy ''it'', all reality will follow."''
-->--'''Owlman''', ''WesternAnimation/JusticeLeagueCrisisOnTwoEarths''

TheMultiverse is a weird thing. Depending on the genre of the work, it can mean a dozen different things. But most sci-fi has a pretty clear definition of what a "Multiverse" is. For every decision someone makes, the universe diverges into several parallel dimensions, one for every possible choice. As such, there are a nearly infinite number of universes where every conceivable version of you (or the lack thereof) exists.

This is a problem for {{Omnicidal Maniac}}s. How can one possibly destroy all of reality if, somewhere, there is ''another'' reality where they fail? The answer is to find Earth Prime: If you find and destroy the ''original'' universe that all others diverged from, you can [[RetGone retroactively destroy all of them]].

Related to ExpendableAlternateUniverse. Compare CosmicKeystone and NoOntologicalInertia. Of course, there are [[TimeyWimeyBall Time Travel Paradoxes]] and {{Logic Bomb}}s abound in this theory, so it definitely requires some WillingSuspensionOfDisbelief. Theoretically, the very act of doing that, would simply create ANOTHER infinite number of possibilities. Therefore, destroying everything ''should'' be impossible.

'''Warning''': May be some spoilers ahead.

* In Anime/YuGiOhArcV it is revealed that [[spoiler:each of the spin-offs is an alternative dimension but the Arc-V world called the standard is the original.]]

* As of ''ComicBook/FiftyTwo'', the Creator/DCComics multiverse hinges on "New Earth" - not just a specific universe, but a specific planet in that universe. This becomes a plot point shortly afterwards in the ''ComicBook/SinestroCorpsWar'', where Sinestro wants to conquer Earth for this very reason.
** Interestingly, DC's comic multiverse has generally not run on the constant temporal divergence model; ''Comicbook/CrisisOnInfiniteEarths'' established that the universes of the pre-Crisis multiverse diverged at the Big Bang, making ''that'' the point to attack, while ''52'' established that the new multiverse began as 52 identical Earths that got cosmologically edited.
** Note that "Earth Prime" refers to another universe altogether that's like ours, where superheroes don't exist outside of comics. In some stories, it ''is'' "our" Earth for all intents and purposes. And it '''was''' actually destroyed in ''ComicBook/CrisisOnInfiniteEarths''. It came back as Earth-33 of the DC multiverse in ''Comicbook/TheMultiversity''.
--> '''[[WebVideo/AtopTheFourthWall Linkara]]:''' Yeah, that wave of antimatter that completely annihilated the universe was a bitch to clean up the next day, let me tell you!
* The ''[[ComicBook/SonicTheHedgehog Sonic]]'' comic book has Mobius Prime, which all other parallel worlds (called Zones) are based off. Interestingly, despite the franchise starting with video games, Mobius Prime is the comic's Zone and not the one of the games.

* The ''Fanfic/PonyPOVSeries'' chapter "Applejack's Dream" establishes the existence of a "Heart World" from which the Pony POV Series world and all other AlternateTimelines diverged from and which anyone still connected to is affected by, implied to be the main series timeline. However, in an interesting twist, it is possible for a world to "break off" and continue on its own without any connection to the Heart World. The plot of that chapter involved preparing for the possibility that would happen so as to [[spoiler:prevent Applejack from going insane and turning into Nightmare Mirror in the event that it did.]] [[spoiler:This later bites Nightmare Eclipse in the flank when her plan has basically made her the Heart World Nightmare Eclipse, and tied all her other selves to her -- in other words, defeating her defeats ''all'' versions of her.]]

* Present in ''Literature/TheHitchhikersGuideToTheGalaxy1''. Vogon Jeltz, tasked with demolishing the Earth, is deemed unsuccessful by his superiors because he only demolished ''one'' Earth, whereas in fact there are millions of others still existing in alternate universes. At the end of ''Literature/MostlyHarmless'', he finally succeeds in eliminating every single one.
* In Creator/GuyGavrielKay's ''Literature/TheFionavarTapestry'', Fionavar is a fantasy version of this; one world that all other ones spring from and depend on.
* In ''Literature/TheChroniclesOfAmber'', this is what makes Amber so special - it's the primal reality which defines the cosmos.
* Creator/WilliamShatner's ''Quest for Tomorrow'' series introduces this concept in the last novel prior to the reboot. In fact, the main characters' goal ''is'' to reboot their reality by altering the result of a coin flip in the prime reality. Unfortunately, Shatner abandons the series two books after the reboot.

* In the movie ''WesternAnimation/TurtlesForever'', when the Utrom Shredder realizes that there are literally hundreds of Franchise/TeenageMutantNinjaTurtles across the multiverse, he decides to destroy them all by defeating the versions from Turtle Prime; that is, those from [[ComicBook/TeenageMutantNinjaTurtlesMirage the first issue of the original Mirage comic]].
* ''WesternAnimation/JusticeLeagueCrisisOnTwoEarths'' has [[StrawNihilist Owlman]], who wants to [[EarthShatteringKaboom use]] [[SwordOfDamocles the QED]] on Earth Prime, thus wiping out all life.