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

The {{Multiverse}} 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 AllTheMyriadWays. 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.

!! Examples
* 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.
* Present in ''Literature/TheHitchhikersGuideToTheGalaxy''. 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.
* As of ''ComicBook/FiftyTwo'', the DCComics multiverse hinges on "New Earth" - not just a specific universe, but a specific planet in that universe (note that "Earth Prime" refers to another universe altogether that's like ours, where superheroes don't exist outside of comics). This becomes a plot point shortly afterward in ''SinestroCorpsWar'', where Sinestro wants to conquer Earth for this very reason.
* In ''Literature/TheChroniclesOfAmber'', this is what makes Amber so special - it's the primal reality which defines the cosmos.
* WilliamShatner's ''QuestForTomorrow'' 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.

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