During the Silver and Bronze Age of Comics spanning the 1950s to the 1980s, Earth-One was the DC Multiverse's primary universe. Earth-One was the universe where the most iconic, most widely recognized versions of DC's characters resided and had their adventures for thirty years.
After CRISIS ON INFINITE EARTHS, all of the Multiverse's worlds, including Earth-One, were folded into a new, Post-COIE DC Earth-DCU. This Earth-DCU probably most resembled Earth-One of the five final universes to be destroyed in the Crisis (the others being Earth-Two, Earth-4, Earth-S, and Earth-X), but was still distinct from Earth-One (i.e. the Superman and Wonder Woman of Earth-DCU were similar to, but also very different from the Superman and Wonder Woman of Earth-One), and this point was emphasized in INFINITE CRISIS last year. Despite some initial confusion, Alexander Luthor recognized that the Earth that emerged after the first Crisis was not Earth-One, and never was. That leaves the question...what ever happened to Earth-One?
When Alexander Luthor attempted to re-create the Multiverse in INFINITE CRISIS, a number of the previously destroyed universes briefly re-emerged....Earth-Two, Earth-S, etc. The world that Alex and the others assumed to be Earth-One, however, was nothing of the sort. When the Earth-Two Wonder Woman returned briefly to speak with her younger counterpart in INFINITE CRISIS, the older Diana was speaking to the Diana of Earth-DCU...the one first written about by George Perez in 1987, not the Earth-One Wonder Woman who was destroyed at the end of COIE (what happened to the memory of that Earth-One Wonder Woman?). When Kal-L fought Kal-El in INFINITE CRISIS, he seemed to be aware that this Kal-El was *not* the Kal-El whose cousin Supergirl died during the first Crisis, and who had teamed up with him so many times before in the past.
In the WHO'S WHO series published back in 1986, entries were included for the Golden Age (Earth-Two) and Modern Age (Post-COIE) versions of the characters, but the Silver/Bronze Age (Earth-One) versions were neglected.
As a fan who grew up with Earth-One DC, it's a little sad to see Earth-One always getting the short end of the stick even when DC goes out of its way to acknowledge its Pre-COIE history.
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