The CW's Crisis On Infinite Earths mini-series is multiverse-spanning story of DC's continuity canon. The 1986 Crisis On Infinite Earths comic book story by Marv Wolfman and George Pérez is famous for establishing DC's multiverse of alternate continuities, with the story used to consolidate them into a single continuity, though DC Comics would eventually return to telling Elseworlds and alternate universe stories within a few years. The CW's Crisis On Infinite Earths adapts the iconic story for the Arrowverse timeline, but serves the inverse function of essentially bringing all DC movies and TV shows under a collective multiverse umbrella.
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