What was the Crisis on Infinite Earths?
The Crisis on Infinite Earths was a 12-issue series published by DC in 1985-6. The “Crisis” effectively revamped the entire DC Universe by merging several universes (containing the various DC characters) into a single universe (whose history is still somewhat unclear in parts). The Crisis was used as an opportunity to change DC history retroactively (see “retcon” in the list of definitions in part 2), including the remaking of several main DC characters. Thus people refer to the “post-Crisis” Superman, Wonder Woman, etc., as distinct from the “pre-Crisis” versions who existed on “Earth-1” (Silver Age) or “Earth-2” (Golden Age). The confusion *really* begins because the revamping and “retconning” didn’t all take place in the Crisis limited series itself, nor in the comics immediately after then. If DC had simply started all their series over from scratch, things would have been pretty straightforward. Instead, they declared the Pre-Crisis history to be implicitly intact, until and unles