My earlier post, History of the DC Universe: 1935-1985, breaks down how DC Comics became committed to a shared and (relatively) consistent continuity very gradually over a period from about 1952-1969. But once a shared universe began, inconsistencies from older stories were left unresolved and new ones were being made all the time. In 1981's Green Lantern #143, writer Marv Wolfman answered a letter from a fan who asked about why a character from Kamandi's universe had recognized Hal Jordan in a sprawling crossover in Showcase #100, but claimed not to in a recent issue of GL. Wolfman's answer acknowledged a need for some sort of clean-up wherein editorial powers would make it clear which past events were part of the main (Earth One) continuity and which weren't. At about the same time, some creators at DC began to perceive that the idea of a Multiverse was too confusing for new readers, and some features, such as Superman, seemed to be in need of a major overhaul. And thus, DC's first housecleaning event, Crisis on Infinite Earths, was conceived. It would finally be published in 1985-1986, and created a new, simpler, better DC Universe.
But if a shared, moderately consistent DC Universe was only about 15 years old when Wolfman saw the need to simplify it, it took much less than that for the need to arise for another clean-up, event, which was followed by another, and another. The post-1985 history of DC Comics is most aptly summarized by recording these reboot events, and what effect they had. They are as follows:
1986: Crisis on Infinite Earths
1994: Zero Hour
2006: Infinite Crisis
Each of these events restarted or revised the timeline of the DC Universe, enabling them – in principle – to change everything. In practice, none of them led to a completely new continuity. COIE and Infinite Crisis performed radical surgery on the Multiverse, with the former reducing the number of alternate Earths from "Infinite" down to just one, and the latter event increasing the number from one up to 52. Infinite Crisis made a modest number of changes to the continuity of the main Earth, while Zero Hour performed some extremely limited clean-ups. Below, I break down in more detail the changes that each reboot ushered in:
Crisis on Infinite Earths
In principle, Crisis rebooted everything. A new timeline began, and the Multiverse never existed in this timeline. In practice, many features were rebooted with new origins while other features were affected only slightly.
• The Multiverse of many alternate Earths was replaced by just one positive-matter universe with a past history that consisted primarily of a modified version of the Silver Age continuity of the Justice League and other Earth One features in its recent past and distant future, preceded by a modified version of the Golden Age continuity in its World War Two era. A smattering of heroes from other Earths were added to the modern age of post-Crisis Earth.
• Superman and Batman lost their positions of prominence as among the first superheroes on both Earth One and Earth Two. Instead, the JSA era had no versions of Superman and Batman at all, and they became first heroes of the second wave, but reserve members of the JLA instead of founding members.
• Superman's history was completely overhauled, with the Byrne Superman constituting a significantly new version of the character.
• The original lineup of the Justice League became Flash, Green Lantern, Aquaman, Martian Manhunter, and Black Canary. Superman and Batman existed at that time, but did not join as full-time members of any version of the Justice League until later.
• Wonder Woman was, in time, retconned to be two people: Diana's mother Hippolyta as a member of the JSA and Diana coming along much later as a member of the third lineup of the Justice League.
• Characters such as Captain Marvel of Earth-S, Blue Beetle and the Question of Earth-Four, and Lady Quark were added to the current era of superheroes.
• The Crisis itself became part of post-Crisis Earth's history, but as an attack by the Anti-Monitor on the one and only positive-matter universe. Barry Allen died in this Crisis, but Supergirl, who had never existed, did not.
• Many characters, including Donna Troy, Power Girl, and Hawkman, were eventually rebooted at least once, in an effort to provide them with histories that were consistent with the new, unified Earth.
• Because the new Superman had never been Superboy, the Legion of Super-Heroes were inspired by the Superboy of a Pocket Universe that was created as part of a nefarious plan by the Time Trapper. A sequence of timeline reboots taking place in – and affecting only – the Thirtieth Century created more than one new, distinct version of the LSH.
• Because certain features, such as Wolfman and Perez's own Teen Titans, were not rebooted, the post-Crisis continuity of these features was added on to pre-Crisis continuity, which eventually became very lengthy and complex.
• Justice League continuity eventually included six considerably distinct lineups: The Year One JLA, the Detroit JLA, Justice League International and Justice League Europe, the new Big Seven with Kyle Rayner and Wally West, and a new JLA led by "the Trinity" of Superman, Batman, and Wonder Woman, which eventually turned into the Robinson JLA with Donna Troy, Starman, and Congorilla. This slate was wiped clean only with Flashpoint.
• The ranks of youths who served as Robin eventually included Dick Grayson, Jason Todd, Tim Drake, Stephanie Brown, and Damian Wayne. This sequence of Robins has never been reset at any point from 1940 to the present.
In principle, Zero Hour also restarted the timeline, and modest retcons affected some features, such as Batman, but no flagship features were fundamentally altered. A fold-out in the final issue included a timeline of the DC Universe.
Infinite Crisis became the third event to reconstitute DC continuity. The villains' effort to remix pre-Crisis Earths to their liking was thwarted, resulting in a haphazard reordering of continuity of no one's design. A few major changes resulted:
• Superman, Batman, and Wonder Woman were once again made full founding members of the original Justice League lineup, replacing Black Canary in that capacity.
• DC once again had a Multiverse, rather than only one dimension. The new Multiverse, however, was not revealed for almost a year after Infinite Crisis ended, and has only 52 Earths rather than the thousand (or "infinite") Earths before COIE. These were initially identical, but tampering by Mister Mind made them all distinct. Many of these Earths were described only in very brief fashion until nine years later, when the Multiversity Guidebook provided an overview of almost all of them.
• In general, Infinite Crisis left more things the same than it changed, but it gave writers latitude to make modest changes that they could explain as having happened as a result of the event, or of Superboy Prime having altered reality while punching the walls between dimensions. Consequently, many small changes were revealed months and years after the event ended.
Only five years after Infinite Crisis, Flashpoint changed DC Comics in more radical fashion. In contrast to COIE, which was published long after the concept was considered, Flashpoint apparently occurred as a matter of some urgency, interrupting many creative projects mid-stride. This was perhaps most evident in the Dark Knight title, which ran only 5 issues in a Volume 1 before being rebooted with a new #1. The New 52, as the post-Flashpoint DC Universe was called, made dramatic changes in the publication format as well as fictional, creative changes within the story:
• DC began distributing new comics digitally on the same day that print versions were released.
• Every title, new or old, was relaunched with a new #1, including the venerable Detective, Action, Superman, and Batman, which had not previously been renumbered since their 1937-1940 inceptions.
• Most flagship characters received a new costume, in many cases raising the collar, creating a 3-D armor look in place of skintight fabric, and eliminating the "underwear on the outside" look that had traditionally added an extra splash of color to the uniforms of Superman and Batman.
• The timeline of the main Earth, Earth 0, was rebooted in significant ways, although those have not yet been entirely explained. Most notably, the Justice League was rebooted with a new origin depicting the first meeting of most of the various pairs of heroes, including Superman and Batman, but not Flash and Green Lantern. New origins were told for many characters, including Superman, Batman, and Wonder Woman, but significant elements of their pre-Flashpoint history appear to be intact. The main heroes are now shown as almost a decade younger than in their pre-Flashpoint versions. Details of how much pre-Flashpoint history is still in continuity continue to emerge as new stories are published.
• Earth 2 was radically reimagined, replacing a version in the image of the Silver Age Earth-Two which had been seen only occasionally after Infinite Crisis with a new version stricken by bloodshed and catastrophe. A relentless series of attacks by Darkseid first eliminated the new Earth 2's versions of Superman, Batman, and Wonder Woman, then almost the entire population, and finally the physical planet itself. The survivors now live on a new planet along with superheroes loosely based on the members of the Justice Society.
• The rest of the Multiverse is presumably unchanged since Mr. Mind created it at the end of 52. Most of this was seen rarely or not at all before Multiversity in 2014, so there was no creative reason to change any of the Earths besides Earth 0 and Earth 2.
Five Versions of History
In, all, DC has had about five major company-wide versions of continuity in their main storytelling world, and countless parallel worlds, alternate timelines, and lesser retcons. To describe the full history would occupy an encyclopedia, but a quick summary can be provided by listing some of the major superheroes of the era in approximate order of introduction, and the various incarnations of the "J" teams (Justice Society / Justice League). Other features, other reboots, and the tangled history of the future and past are beyond the scope of this summary.
Golden Age (1938)
Superman, Crimson Avenger, Batman, Sandman, Flash, Hawkman, Hour-Man, Spectre, Doctor Fate, Green Lantern, Atom, Justice Society, Aquaman, Green Arrow, Wonder Woman, Seven Soldiers of Victory.
Silver Age (1952)
Earth One: Superman (first as Superboy), Batman, Wonder Woman, Aquaman, Green Arrow, Martian Manhunter, Flash, Green Lantern, Justice League, Atom, Hawkman. After many years, original JLA replaced by Detroit version.
Earth Two: Retroactively declared to fit the Golden Age stories, with considerable revisions made or implied. The JSA returned from retirement and younger heroes began another team, Infinity Inc.
World War Two era: Flash (Jay Garrick), Sandman, Green Lantern (Alan Scott), Wonder Woman (Hippolyta), Hawkman (Carter Hall), Doctor Fate, Atom (Al Pratt), Black Canary, Justice Society.
Second era: Superman, Batman, Flash (Barry Allen), Green Lantern (Hal Jordan), Martian Manhunter, Aquaman, Black Canary (II), Justice League (with Black Canary but without Superman, Batman, or Wonder Woman). Detroit Justice League. Flash (Wally West). Justice League International and Justice League Europe. Wonder Woman (Diana), Green Lantern (Kyle Rayner). "New Big Seven" Justice League.
Post-Infinite Crisis (2006)
This timeline inherited most of the Post-Crisis timeline, but with the original Justice League reset to the Silver Age lineup with Superman, Batman, and Wonder Woman instead of Black Canary. After Infinite Crisis, a new JLA lineup included several Silver Age JLAers along with Red Tornado, Black Lightning, Vixen, and Arsenal (Roy Harper). This later gave way to a JLA lineup including several former Teen Titans, Congorilla, and Starman (Mikaal Tomas).
New 52 (2011)
Earth-0: Superman, Batman, Wonder Woman, Martian Manhunter, Aquaman, Flash, Green Lantern, Cyborg, Justice League.