Multiverse (DC Comics)
Led by editor Julius Schwartz and writer Gardner Fox, DC Comics' superheroes were given a "reboot" with the publication of Showcase #4 in 1956, where a new version of the Flash made his first appearance.
The success of this new Flash led to the creation of new incarnations of the Golden Age characters who only shared the names and powers but had different secret identities, origins and stories.
It helped (among other things) to explain continuity errors, to retell and retcon stories, and to incorporate foreign elements that could actively interact with everything else and allow them to have an "existence".
The way used to circumvent some of these errors was the "Multiple Earths", which also showed a chaotic nature that brought even more continuity problems that were not easily explained or were simply left unexplained.
The resulting universe had a slightly re-written story with no continuity errors even though it was acknowledged that reality-shattering events did happen (including the Crisis on Infinite Earths).
In 1999, the unexpected and overwhelming success of Elseworlds' Kingdom Come and other stories, led to the creation of the concept known as Hypertime in order to publish crossovers with those characters and the mainstream continuity.
Hypertime was similar to the former Multiverse as it allowed each and every reality ever published to co-exist and interact as most branches tend to return to the original stream (explaining some retcons as well as crossovers).
In the miniseries, Milestone Forever, in a similar fashion as Captain Atom: Armageddon, the events that led to the end of the Dakotaverse and its integration to the new DC continuity are revealed.
In addition, as most of the history of the Modern Age was still being the main continuity, younger readers could not follow the stories of the mainstream versions of the DC heroes, just as had happened prior to the original Crisis on Infinite Earths.
[8][9] It is revealed in Doomsday Clock that the New 52 was created by Doctor Manhattan as he experimented with reality, manipulating events to prevent many Golden Age heroes from gaining their powers and continually moving Superman to different points in the timeline, resulting in superheroes emerging later in history.
After a confrontation with Superman, Manhattan attempts to erase his tampering and restore the Pre-Flashpoint and Pre-Crisis multiverses, as well as elements he had previously removed from the history of Earth-0 such as the Justice Society of America and Legion of Superheroes.
The resolution to the Perpetua story arc was advertised in Justice League #39 as "The Encore", which would eventually be published as Dark Nights: Death Metal.
In an epilogue published in The Flash #750, Wally surveys the timestream and notices multiple contradictions and inconsistencies within history, the result of Manhattan's reckless tampering with time.
This was originally intended to lead into the Generations miniseries and a reboot of the Multiverse termed "5G", which would have fixed all of DC's publishing history into a single coherent continuity, stretching from World War II to the present day, with stories going forward focussing on new characters or aged versions of current ones.
Only by "tuning" to the specific frequency of a universe could a person leap to another Earth, as Barry Allen discovered as he tried to perform a disappearing act by vibrating his molecules at super-speed (Flash #123).
The "speedster" later developed a machine called the "Cosmic Treadmill", which, when it was used by people who controlled the Speed Force, it allowed the users to trespass the "vibrational barriers".
Several elements that have appeared across the history to what now is DC Comics have also been actively incorporated in the new structure, such as the Source Wall (The New Gods), the Bleed (Wildstorm's The Authority), the Speed Force and the vibrational barriers (The Flash) and the Rock of Eternity (Shazam!).
In that dimension, Clark Kent encounters another version of himself who is a human biological son of Martha and Jonathan and never met Lana Lang (who is a cheerleader with a different group of friends).
Also in this dimension, Chloe Sullivan is engaged, Lana Lang is a married woman living in Paris, Sheriff Nancy Adams left Smallville and works as a member of the government, and Lex Luthor became President of the United States.
In the fourth issue of the television series' comic book continuation Smallville Season Eleven, an alternative version of Chloe Sullivan from Earth-2 arrives to Clark Kent's world and reveals that her universe is destroyed before her death.
The storyline of Injustice: Gods Among Us features an alternate reality where the Joker has tricked Superman into killing Lois Lane and their unborn son and destroying Metropolis with a nuclear explosion.
Kara is tasked with watching over her baby cousin Kal-El and flees Krypton in a spaceship at the behest of her mother; however, her ship is damaged and knocked off course by the planet's explosion, which puts her into suspended animation.
Meanwhile, Bruce is busy with the rebuilding the world after the Regime, forcing him to enlist other heroes such as the Black Canary, her husband the Green Arrow (from the alternate universe that the Black Canary was sent to by Doctor Fate), Firestorm and the Blue Beetle/Jaime Reyes as well as Harley Quinn, the Flash (who had been pardoned due to his role in taking down the Regime after the murder of Billy Batson by Superman) and Hal Jordan, who was reinstated as Green Lantern by the Guardians of the Universe, who managed to rehabilitate him.
The Batman tasks the Black Canary, the Green Arrow, and Harley to deal with the Society, a group of supervillains formed by Gorilla Grodd after the fall of the Regime.
During the events of the tie-in comic book Infinite Crisis: Fight for the Multiverse, it is said that the Monitors were a race of beings native to the world of Nil that resided outside all realities in the Overvoid.
In 2014, DC CCO Geoff Johns said that the universe present in the publisher's television series, Arrow and The Flash, is separate from the one being built in their films with Man of Steel and Batman v Superman: Dawn of Justice.
The Multiverse concept is explored during the second season of The Flash, which is pivotal to the conflicts between Barry Allen (Grant Gustin) and rogue speedster Hunter Zolomon (Teddy Sears).
In the episode "Enter Zoom", it is revealed that Earth-2's version of the Green Arrow is Robert Queen (Jamey Sheridan) instead of his son Oliver (Stephen Amell), who presumably died on the boat accident.
In the season two finale "The Race of His Life", Zoom reveals that the universe in which that of Arrow, The Flash and Legends of Tomorrow sets is positioned in the Multiverse's center, and from there one could travel to any of the other infinite numbers of Earths.
The 2017 crossover event "Crisis on Earth-X" – which sees the heroes from all four shows face an invasion from the titular 'Earth-X', as a world where the Nazis won World War II – establishes that there are 52 known alternate Earths, with the titular 'Earth-X' being the fifty-third Earth, described by Harrison "Harry" Wells of Earth-2, that those who are aware of the multiverse as being so dark and horrific that no interdimensional traveler would dare to journey there.
