The title of the series was inspired by earlier crossover stories involving the multiple parallel Earths of the Multiverse, such as "Crisis on Earth-Two" and "Crisis on Earth-Three", but instead of lasting two to five issues and involving members from as many superhero teams from as many parallel worlds, it involved virtually every significant character from every parallel universe in DC's history. It in turn inspired the titles of seven subsequent DC crossover series: Zero Hour: Crisis in Time (1994), Identity Crisis (2004), Countdown to Infinite Crisis (2005), Infinite Crisis (2005-2006), 52 (2006-2007), Countdown to Final Crisis (2007-2008) and Final Crisis (2008).
These issues were addressed during the Silver Age by DC creating parallel worlds in a multiverse: Earth-One was the contemporary DC Universe, which had been depicted since the advent of the Silver Age; Earth-Two was the parallel world where the Golden Age events took place, and where the heroes who were active during that period had aged more or less realistically since that time; Earth-Three was an "opposite" world where heroes were villains, and historical events happened the reverse of how they did in real life (such as, for instance, President John Wilkes Booth being assassinated by a rebel named Abraham Lincoln); Earth Prime was ostensibly the "real world," used to explain how real-life DC staffers (such as Julius Schwartz) could occasionally appear in comics stories; and so forth. If something happened outside current continuity (such as the so-called "Imaginary Stories" that were a staple of DC's Silver Age publications), it was explained away as happening on a parallel world, a premise not dissimilar to the company's current "Elseworlds" imprint.
Some have said that, over the years as new readers were introduced to the DC Universe, the "multiverse" theory — with its attendant multiple versions of Superman, Batman, Wonder Woman, et al. — served to confuse those who did not have a working knowledge of DC's history. The editorial objective of Crisis on Infinite Earths was to streamline all of these parallel worlds into a single, consistent backstory, and thus hopefully make the DC Universe more "approachable" to new readers. It was also to free the company's writers from the "baggage" of 50 years of (dis)continuity.
The series was highly successful from a marketing standpoint, generating renewed interest in the company's books, enticing readers with the tagline that "the DC Universe will never be the same." Along with Alan Moore's Watchmen and Frank Miller's Batman: The Dark Knight Returns, it contributed to the commercial and creative revitalization of DC Comics, which had been dominated in the market by rival publisher Marvel Comics throughout the 1960s, 1970s, and early 1980s.
Crisis also helped popularize the formula of the line-wide "crossover" comic book series, a concept first seen in Marvel's Contest of Champions (1983) and Secret Wars (1984). Since 1985, superhero publishers such as DC and Marvel have had frequent "summer crossover" series designed to tie many of their comic book titles together under a single storyline (and thus sell more comic books).
Wolfman came up with an idea which would reach across the entirety of the DC Universe and its 50-year history. First of all, he came up with the character of the Monitor who was initially a faceless character used in many of DC's titles over the course of a year. The Monitor supplied DC's villains with equipment in order to test its heroes for the Crisis ahead. As a result, the character was seen to be a villain himself and his real reasons were not revealed to the reader until Crisis #1.
The story introduces readers to two near-omnipotent beings, the good Monitor and the evil Anti-Monitor, who had been created as a result of the same experiment that created the Multiverse. The Monitor made cameo appearances in various DC comic book series for two years preceding the publication of the series and at first appeared to be a new supervillain, but with the onset of the Crisis, he was revealed to be working on a desperate plan to save the entire Multiverse from destruction at the hands of the Anti-Monitor. The Crisis series highlighted the efforts of DC Comics' superheroes to stop the Anti-Monitor's plan. Under the initial guidance of the Monitor, a select group of heroes was assigned to protect massive "tuning forks" designed to merge the surviving Earths into one that could be protected from the antimatter that had already annihilated untold numbers of alternate Earths. Eventually the conflict grew, and nearly every DC hero became involved in the battle.
The Monitor was murdered by his own assistant, Harbinger, while she was temporarily possessed by one of the Anti-Monitor's "shadow demons". However, he expected the attack and allowed it to happen so his death would release enough energy to protect the last five parallel Earths (the homes of the known DC Universe) long enough for the heroes to lead an assault on the Anti-Monitor, under the guidance of the Monitor's assistants, Harbinger, Alexander Luthor, Jr., and Pariah. The villain is forced to retreat, but at the cost of Supergirl's life.
This lull in the war provides some breathing room for the heroes, but the various supervillains join forces under Brainiac and Lex Luthor to conquer the Earths, while the Anti-Monitor causes chaos on the Earths by forcing the Psycho-Pirate to manipulate the emotions of their inhabitants. The second Flash dies stopping the Anti-Monitor's backup scheme of destruction (to use an antimatter cannon to penetrate the protective aura). The Spectre halts the hero/villain conflict, warning that the Anti-Monitor is traveling to the beginning of time to prevent the Multiverse's creation. Heroes and villains join forces in response with the heroes traveling to stop the Anti-Monitor, and the villains traveling to the planet Oa in antiquity to prevent the renegade scientist Krona from performing a historic experiment that would allow the Anti-Monitor to succeed in his efforts.
The villains fail, and Krona proceeds with his experiment, while the heroes support the Spectre, whose battle with the Anti-Monitor creates an energy overload that shatters space and time. With that, a single universe is created and all the superheroes return to a present-day reality where the various elements of the five Earths were fused into one, with no one except the people present at the battle at the dawn of time remembering the original reality.
The Anti-Monitor attacks one last time, transporting Earth to the Anti-Matter universe and summons a massive horde of shadow demons. However, he falls to a carefully planned counter-attack, culminating in a battle with Kal-L (the Earth-Two Superman), Alexander Luthor of Earth-Three, and Superboy of Earth-Prime, with some unexpected last-second help from the New Gods' adversary, Darkseid. As the Anti-Monitor crashes into a star and dies, Alex sends himself, Earth-Two Superman, Earth-Two Lois Lane, and Earth-Prime Superboy into a paradise reality.
The aftermath of the crisis plays out a few pages later, including Wally West becoming the new Flash. The final page shows the Psycho-Pirate, who was now imprisoned in Arkham Asylum, talking to himself in a monologue:
I'm the only one left who remembers the Infinite Earths. You see, I know the truth. I remember all that happened, and I'm not going to forget. Worlds lived, worlds died. Nothing will ever be the same. But those were great days for me... I had a good friend in the good old days, really. He was the Anti-Monitor. He was going to give me a world to rule. Now he's gone, too. But that's okay with me. You see, I like to remember the past because those were better times than now. I mean, I'd rather live in the past than today, wouldn't you? I mean, nothing's ever certain anymore. Nothing's ever predictable like it used to be. These days... y-you just never know who's going to die... and who's going to live.|||Psycho Pirate|Crisis on Infinite Earths #12, p.42
If this idea had been used, the Man of Steel would have proclaimed the return of the "Original Super-Hero" as Kal-L (now switched to Kal-El) began his life on the Post-Crisis Earth that is similar to his old life, but was completely different, such as how different this version of Lois is and how differently this version of Batman behaves towards him. Despite this "culture shock", Kal-L endured and was given a new lease on life by being deposited back to the early days of the modern heroic age of the Post-Crisis Earth. However, this was discarded when the John Byrne version of Man of Steel was planned.
Crisis was used by DC as an opportunity to wipe much of its slate clean and make major changes to many of their major revenue-generating comic book series. Frank Miller's revamp of Batman with Batman: Year One, George Pérez's relaunching of Wonder Woman (see Gods and Mortals), and John Byrne's reboot of Superman (see The Man of Steel) all took place shortly following Crisis on Infinite Earths, and changed substantial elements of the characters' backstories.
Several other titles which were not significantly retconned were taken in very different directions following Crisis. The Flash was relaunched starring a younger main character, the previous Flash's sidekick, Kid Flash (also known as Wally West). Green Lantern was briefly changed to Green Lantern Corps, chronicling the adventures of a group of Green Lanterns led by Hal Jordan and stationed on Earth. The Justice League of America title was cancelled, to be replaced by a new series entitled simply Justice League, featuring a new and uniquely diverse cast, many of them drawn from what had been different universes in DC's pre-Crisis multiverse. While some of these revamps of classic superheroes were less successful than others, their new beginnings can generally be attributed to the success of Crisis on Infinite Earths.
The majority of DC Universe characters are unaware that the original, multiverse-wide Crisis on Infinite Earths occurred. Although the characters who were present at the epic battle at the dawn of time (Crisis on Infinite Earths #10, "Death at the Dawn of Time") - Psycho-Pirate, Lady Quark, Harbinger, and Pariah - were initially treated as exceptions, this idea did not stick. There have been occasional references to the event. A 2002 storyline in the Supergirl comic book saw the original pre-Crisis Supergirl landing on post-Crisis Earth, for example, and established that the Spectre, being able to see across dimensions and timelines, is aware the Crisis occurred. In addition, Grant Morrison's run on Animal Man, heralded for its deconstruction of the concept of the comic book, initiated a "Second Crisis" in which characters such as the original Crime Syndicate of America from Earth-Three came back to life thanks to the Medusa Mask owned by the Psycho-Pirate, who remembered the original Crisis. Per Degaton is aware of the pre-Crisis timeline; he told the JSAs of the present and of 1951 that he would retcon them out of existence the same way the Huntress of Earth-Two was. With the Fourth World existing outside the Multiverse proper, Darkseid has also acknowledged the events of the Crisis. Members of the Green Lantern Corps were also aware of the Crisis, even though none participated in the battle at the beginning of time. Corps member Ch'p, the only Earth-One character to have his timeline completely erased by the Crisis, was nonetheless recognized by his fellow Green Lanterns. John Constantine is also aware of the Crisis, as seen in Swamp Thing vol. 2, issue 70; additionally, a folder titled "Crisis" was seen in Constantine's possession in Hellblazer issue 10. Finally, in the Planetary special Planetary/Batman: Night on Earth, it was implied that Elijah Snow had somehow temporarily left the Wildstorm universe to witness the Crisis.
Some of the dead characters reappeared or disappeared in some way later:
After the Crisis, former Kid Flash Wally West took over the mantle of his predecessor The Flash. Jonah Hex was transported to a post-apocalyptic future but this did not prove popular and subsequent stories brought him back to the Wild West. The JSA member Wildcat was briefly replaced by his god-daughter, Yolanda Montez. The Guardians of the Universe departed for an unknown dimension, and the Green Lantern Corps was reorganized, with Hal Jordan leading a team of Green Lanterns based on Earth. Further, the Black Canary character was split into two persons – the "original" Black Canary (Dinah Drake Lance) and the "new" Black Canary (Dinah Laurel Lance, daughter of the original).
The new version of Hawkman did not appear until 1989; this raised questions about the character who had been appearing with the post-Crisis heroes since 1986. Similar problems faced the Legion of Super-Heroes, which had been affected by the removal of Superboy from continuity. Two female characters, Donna Troy and Power Girl also encountered continuity problems in the new DC universe. In 1994, DC's mini-series Zero Hour attempted to resolve these conflicts by again rebooting the DCU, this time with fewer wholesale revisions.
The erasure of Superman's cousin Supergirl from DC continuity was slowly revised in the years after 1986; a variety of characters named Supergirl were introduced. In 2004 DC introduced a Supergirl whose background closely matched the pre-Crisis Kara Zor-El of Krypton.
An untold story from Crisis on Infinite Earths was published in Feb. 1999 as a special in the Legends of the DC Universe: Crisis on Infinite Earths #1, written by Crisis writer Marv Wolfman with art by Paul Ryan and Bob McLeod. This untold story's timeline took place during and after Crisis on Infinite Earths #4.
The Flash of Earth-D, Rei was a Japanese man who idolized Barry Allen, whose stories only existed in comic books. Rei was inspired by Allen to become the Flash, much like Allen was inspired to become the Flash by his idol, Jay Garrick. Allen and Rei met during the Crisis on Infinite Earths when Barry was coming back from the 30th century and arrived in the wrong universe. As that earth was under attack by the shadow demons, Barry called on the Justice League and Tanaka called on the Justice Alliance, his world's version of the Justice League. They built a cosmic treadmill and made an evacuation. The Justice League left, but 39 seconds later, Earth-D perished.
This was the only appearance of Earth-D, an earth that was never revealed to have existed prior to this Legends of the DC Universe special.
The first wave includes action figure representations of Earth-2 Robin, Supergirl, the Monitor, Harbinger, and Psycho Pirate. The second wave includes action figure representations of the Flash (Barry Allen), Earth-2 Superman, the Anti-Monitor, Lex Luthor and Brainiac. A third wave has been recently released and includes action figure representations of Earth-Prime Superboy, Batman, a Weaponer of Qward, Earth-2 Huntress, and the female Dr. Light. There is no word at this time whether or not a fourth wave of figures are in the works.