Post-Crisis

"Post-Crisis" describes the state of The DCU after Crisis on Infinite Earths, in which all of the various Alternate Earths were either destroyed completely or melded into a single compound timeline, and various characters' histories were shuffled around, rebooted, or erased completely. One would speak of, for example, the Post-Crisis Superman, as opposed to the Pre-Crisis Superman. Essentially a narrative device to change what was Canon, and one of the first Cosmic Retcons in comics.

The Post-Crisis universe has been rewritten many times since CoIE. Zero Hour, a Crisis Crossover from 1994, was meant to resolve the various inconsistencies that had been introduced since CoIE; it failed. Later, the concept of Hypertime was introduced to substitute for the lack of Alternate Universes; it failed. The latest Cosmic Retcon is Infinite Crisis, bringing back some of the concepts jettisoned in the original.

Compare with the New 52, DC's second complete overhaul.

Some of the changes which occurred Post-Crisis:
 * Superman
 * Superman's revised origin was told in the miniseries The Man of Steel, by John Byrne. Later, this origin was revised again, in Birthright, by Mark Waid; and yet again, in Secret Origin, by Geoff Johns.
 * Superman's first appearance was not as Superboy, but as an adult, when he first came to Metropolis. (Superboy was retconned back into history by Geoff Johns in 2010). His powers developed gradually, with flight not coming along until his late teens.
 * His powers were also extremely downgraded. At Superman's Pre-Crisis height, he could fly faster than the speed of light, travel through time unaided, move planets with his bare hands, and survive in the middle of a supernova. Attempts had been made before to reduce his overall power level, but this one has largely stuck.
 * His power source was also tinkered with. For years, his powers had come from "the rays of Earth's yellow sun", but how this worked was never very well-defined. Post-Crisis, his body was essentially a living solar battery, charging up over the years since he was born on Earth (thus accounting for his slowly-developing powers as a child). Nowadays, before doing a real super feat, Superman will sometimes take a moment to charge up with extra solar radiation beforehand. There were also hints that some of his powers might be psionic in nature, such as his observation that it was much easier for him to lift large, heavy objects (like cargo ships) while flying than while standing. (These hints would pan out with the appearance of the Post-Crisis Superboy, a clone with telekinetic powers.)
 * Initially, there was only one kind of naturally-occurring kryptonite; green. But by the time of the Crisis, at least a dozen varieties had been added, including White Kryptonite, Jewel Kryptonite, and X-Kryptonite. Immediately Post-Crisis, though, it returned to a single type. However, several other varieties were eventually introduced into the Post-Crisis universe.
 * The major types were reintroduced properly late in the Post Crisis era with the arrival of Superman's cousin Supergirl. The only major change is gold kryptonite which now only causes temporary power loss instead of being permanent.
 * Prior to the Crisis, Superman had been the character's "real" identity and Clark Kent, uberwimp, was just a convenient disguise. Post-Crisis, this was reversed. Both the glasses and the cape were covers for the "real" Clark Kent, the super-powered Midwestern farmer's son that only his parents were privy to. Both personas grew on Clark since his Man Of Steel origin story (where he had insisted Superman was nothing but a fancy costume), with Kent being a competent, sharp-witted journalist (a far cry from the Pre-Crisis loser) with his own life and friends, and Superman developing important personal friendships with other superheroes, most notably Batman, with whom he had a very different relationship than the pre-Crisis best buds. Likewise, no one suspected that Superman had an alter ego (after all, without a mask, who's to assume he's hiding something?), and Lois Lane was no longer obsessed with discovering his Secret Identity. In fact she was often much more interested in Clark as he was the only person who ever managed to scoop her. She also was no longer in love with Superman, and instead slowly developed an attraction to Clark during the early '90s.
 * After Clark Kent became engaged to Lois Lane (and, afterwards, revealed his secret identity to her), he had a Secret Keeper in Metropolis as well as his parents and Lana Lang in Smallville. This caused the distinction between Smallville!Clark and Metropolis!Clark to largely deteriorate (presumably, his friends and coworkers just thought he was getting Character Development). This mode of personality has persisted to this day (although Depending on the Writer, via Armed with Canon, became more pronounced for all DC characters after the Crisis, and therefore some application of Broad Strokes is necessary).
 * Speaking of his parents, before the Crisis, Ma and Pa Kent were deceased; some time in The Silver Age of Comic Books, it was revealed that they died of an alien plague that their adopted son couldn't cure. Post-Crisis, both Ma and Pa were alive and well and still a big part of their son's life. They were also much younger at the time they adopted Clark (Pre-Crisis they were already in their later years) to facilitate the greater impact they had on his adult life.
 * The Earth-2 Superman, who had been a member of the Justice Society of America, was erased from history. (However, he still existed, having been rescued to a haven outside of time, and eventually popped up again in Infinite Crisis.)
 * Lex Luthor was changed from a Mad Scientist to a Corrupt Corporate Executive with a major business backing his evil schemes. The current version is a combination of these two.
 * Krypton changed from simply being humans with more advanced tech (and superpowers) to being a cold sterile society of Absolute Xenophobes. This both explained why the Kryptonians didn't have any spacecraft laying around for evacuation and why Superman thought of himself more as a human than as a Kryptonian. This set the stage for villains like the Eradicator.
 * Likewise Clark did not know he came to Earth in a rocket until he was 18 and didn't know about Krypton until he was 28. Thus he had come to think of himself as basically human but with special abilities.
 * Some of the changes Byrne made hearkened back to the character's original 1938 incarnation. Superman didn't learn about his alien heritage until well into his adulthood, and according to his origin, his powers developed gradually during his teenage years. His career as Superboy was itself originally a retcon of Superman's initial origin story.


 * Supergirl
 * Supergirl was killed off in Crisis on Infinite Earths, but an editorial mandate came down that Superman was to again be the last survivor of Krypton. Thus, for several years Post-Crisis, Supergirl didn't exist (though her Earth-2 equivalent, Power Girl, was kept on and given a new Backstory). Eventually, a new non-Kryptonian Supergirl was introduced. From there, it got complicated. (See Supergirl.) A version of the Kryptonian Supergirl was reintroduced in 2004.


 * Wonder Woman
 * Wonder Woman was treated as essentially a brand-new character, coming to Man's World for the first time. She had no secret identity and no Lois-Lane-esque love interest, and received much stronger ties to Greek mythology. With Infinite Crisis, though, when she came into Man's World was restored to before the JLA was first founded, but the rest of the changes remained.
 * Unlike Superman, she was actually increased in power. She could fly under her own power, and lost several vulnerabilities, such as having her bracelets removed. Furthermore, her compunction against using deadly force was removed (the only one among DC's "big three" that this happened to), making her willing to use that option when she judges it necessary.
 * The Earth-2 Wonder Woman was erased from history. Initially, there had never been a Wonder Woman as part of the Justice Society of America; later, as part of a time-travel adventure, her mother Hippolyta took her place there.
 * In addition, her Rogues Gallery was reimagined to make the members real threats. The key example is the Cheetah, who was changed from a normal woman in a silly cheetah costume to a ferocious were-cheetah who could be a deadly challenge to Diana.


 * Wonder Girl
 * Since Wonder Woman had never existed, her Silver Age protege Donna Troy (who already had a convoluted backstory) was left without a past. Eventually, it was settled that she had been raised and given her powers by the Titans of Greek myth. This worked well until John Byrne, in the Wonder Woman series, retconned in a bunch of extra stuff, including that she'd been created with a magic mirror as Wonder Woman's playmate, kidnapped by one of Hippolyta's enemies in WW's place, and subjected to repeated reincarnation in tragic lives. This was so complicated that shortly after, they killed her off. With Infinite Crisis, she was brought back with a new origin—the merging of all possible Donna Troys from the Pre-Crisis multiverse.


 * Batman
 * Frank Miller told Batman's new origin in the storyline Batman: Year One (as part of the Batman ongoing series). His backstory was much less altered than Superman's or Wonder Woman's, though his weirder Silver Age adventures were quietly removed from continuity. The darker Bronze Age Batman was actually a return to his dark, noir-esque Golden Age days after the kid-friendly stamp of the Comics Code was dropped by DC (to the consternation of no one). While Batman's character was even further darkened Post-Crisis, it was mostly compatible with the Bronze Age version of the character.
 * In Zero Hour, it was stated that the murderer of Bruce Wayne's parents was never caught. Dialogue in Infinite Crisis indicates that this has been retconned out with the murderer, Joe Chill, arrested on the same night for the crime.
 * Also in Zero Hour, the idea of Batman being an "urban legend" was introduced, stating that most people didn't think he actually existed. How true this is held to be has fluctuated. This urban legend part was undone by the 2004 story arc, "War Games".
 * The oddity goes further than that, apparently depending solely on whether they had a Writer on Board. During this timeframe, Bats was also a member of the Morrison JLA, which had billboards featuring the assembled team. Additionally, during the No Man's Land storyline, a big part of the story was given to how Batman had to make public appearances to keep morale for survivors, at one point even making certain to be spotted out and about during the day.
 * He was also no longer a founding member of the Justice League of America.
 * The Earth-2 Batman (who had been dead for several years already) was erased as well.
 * His relationship with Superman, which pre-Crisis had been one of Heterosexual Life Partners and among the most iconic in the DCU, became much tenser and rather antagonistic, although over the course of the years their friendship redeveloped. Unlike many other changes, however, this had some precedent in a Bronze Age rift that they never fully resolved. However, the pervasiveness of Depending on the Writer stopped it from sticking until the Crisis rewrote the history of their relationship.


 * Robin
 * Dick Grayson's history was mostly unchanged, save that his departure as Nightwing was much more acrimonious. Jason Todd, however, was essentially remade into a far different and darker character. Pre-Crisis, Jason Todd had been a near-carbon copy of Dick Grayson; the Post-Crisis version revamped him into a troubled street punk who Batman took in from off the streets.
 * Yes, there was an Earth-2 Dick Grayson, who had kept the Robin identity into adulthood (thankfully with some costume alterations), and yes, he was erased too, right after he was killed off in Crisis On Infinite Earths.


 * The Justice League of America
 * Superman, Batman, and Wonder Woman had no longer been in the JLA (though each eventually joined after Crisis). Black Canary was retconned into having been a founding member. With Infinite Crisis, all three were re-introduced to the team's history.
 * Additionally, Hawkman and Hawkwoman were members, but Hawkman was ultimately three different people. At once. Without any clarity. BEFORE his continuity got really strange.
 * Almost immediately Post-Crisis the humorous Justice League International took place. Notable for two reasons, one being its focus on comedy, the other being its roster. For example the new team had as members Blue Beetle (originally from Charlton Comics), Captain Marvel (originally from Fawcett Comics), Dr. Fate (originally from Earth-2) and Booster Gold (the very first new character created Post-Crisis). Basically it stood as a way showing off their new continuity.


 * The Flash
 * Crisis killed off Barry Allen, the Silver Age Flash, and left Wally West (formerly Kid Flash) becoming the Flash instead. Unlike many post-Crisis changes, this one didn't rewrite a lot of history (other than the characters having existed on the same Earth). Jay Garrick, the original Flash, still existed. Jay and Barry's original universe-crossing meeting was retconned, with Jay's city being frozen in time for an unspecified length of time, and Barry helping to rescue them.
 * It's worth noting that even with an apparent retcon in the works right now, it's heavily implied that all the trouble Barry's in would end if he just went back in time to the Crisis and died like a good soldier.
 * This would be in keeping with the efforts of Crisis writer Marv Wolfman who, not really wanting to kill off Barry, left a back door for Barry to return with a potentially interesting dramatic hook (he is shown bouncing through time during his Heroic Sacrifice and Marv thought it would be interesting to have him pulled out mid-run knowing that he had to return someday to finish his sacrificial run).


 * Green Lantern
 * Hal Jordan's origin is retold in two mini-series, Emerald Dawn and Emerald Dawn II: 90 Days. It established that Hal was trained by Sinestro, until Jordan discovered Sinestro's dictatorship on his home planet of Korugar. These stories have been retconned more recently by Geoff Johns with the "Secret Origin" arc as part of the main series.
 * The origin of the DC Universe was also changed in the 1991 one-shot, Ganthet's Tale. Originally, Krona's attempt to look back at the universe's origin resulted in the creation of the anti-matter universe, as well as the concept of evil into the universe; in Ganthet's Tale, Krona's experiment resulted in him releasing a wave of entropy that shortened the universe's lifespan by a couple of billion years, causing the universe to be "born old".


 * Hawkman
 * The Silver Age Hawkman's origin was retold in the acclaimed 1989 miniseries, Hawkworld, but after it was a success, DC commissioned a Hawkworld regular series to take place where the mini-series left off, resulting in a total reboot of Hawkman's continuity (a la the post-Crisis reboot of Wonder Woman), despite the fact that the Silver Age Hawkman was already established in post-Crisis continuity. Various workarounds were tried, including a claim that previous appearances had been either the Golden Age Hawkman and Hawkgirl or alien spies. Eventually, these became a Continuity Snarl that saw every version of the character disappear from The DCU entirely during Zero Hour; while the Golden Age Hawks were eventually extricated from it, the Silver Age versions are still in limbo.


 * The Legion of Super Heroes
 * Superboy and Supergirl were removed from continuity following The Man of Steel reboot of Superman, which established that Superman was the only survivor of Krypton, and that he started his superheroic career as an adult. This spelled trouble for the Legion, which had originally been inspired by Superboy. They tried several different fixes, including an Alternate Universe Superboy, but Executive Meddling made things more and more confused. In 1994, the Legion continuity was completely rebooted during the Zero Hour Crisis Crossover, and again in 2004 with the "threeboot". In 2007 a version of the original Legion reappeared and the Legion shifted over to this, the "retroboot".


 * Captain Marvel
 * Captain Marvel was completely rebooted, appearing much like Wonder Woman as a new character in The DCU, but his origin remained essentially the same, except for the fact that Billy keeps his youthful personality in his Marvel form. At first, he was the only Captain Marvel, but eventually his long-lost sister became Mary Marvel (who now becomes an adult woman in her Marvel form), and their friend became Captain Marvel Jr. (At one point, they all shared the name of Captain Marvel, calling themselves Captain Marvel 1, Captain Marvel 2, and Captain Marvel 3; only Jr. still uses the name, calling himself CM3.)


 * Charlton Comics Characters
 * The "action heroes" created by Charlton Comics, acquired by DC a few years earlier, were introduced into The DCU, including Captain Atom, The Question, and the Blue Beetle. Captain Atom in particular was altered to the point that he was practically an entirely different character, with his original series retconned in as a cover story for his superhero identity.

This is certainly not the full extent of the changes between Pre-Crisis and Post-Crisis, but it does highlight some of the major characters. Additionally, one of the big issues with the Crisis on Infinite Earths was that, initially, almost nobody remembered the details of it, except for a minor supervillain who was ignored as insane. The problem arose, however, that writers didn't necessarily agree on what did or did not happen, which began the cycle anew.