The multiverse concept has been at the center of the DC Comics Universe for decades. While the Flash is probably the most prominent traveler along the multiverse highway, several other DC superheroes have explored the limitless number of universes in existence.
Events like Crisis On Infinite Earths, Dark Knights: Metal and dozens of other company-wide crossovers have come to define the DC multiverse. However, the Justice League and its allies were crossing universal barriers long before the days of mega crossover events. In the Golden and Silver Ages, a trip through the multiverse and back only took a couple of issues before everything was back to normal again.
10 Wonder Woman Was The First DC Hero To Breach The Multiverse (May, 1953)
Wonder Woman (Vol 1) #59, Written By Robert Kanigher, And Penciled/Inked By Harry G. Peter
"Wonder Woman's Invisible Twin" from May 1953 depicted the Wonder Woman of Earth-One breach the dimensional barrier and travel to an alternate reality. At the time, Diana was being attacked by an unseen presence any time she encountered her own reflection.
When the Lasso of Truth got struck by lightning, Wonder Woman was transported to a parallel Earth. Diana encountered Tara, this alternate world's Wonder Woman. Here, the Amazons had been conquered, and Tara was leading a battle for their freedom. The two Wonder Women teamed up to free the Amazons, and Wonder Woman returned to her native Earth.
9 Green Lantern Travels To The Antimatter Universe (October, 1960)
Green Lantern (Vol 2) #2, Written By John Broome, Penciled By Gil Kane, Inked By Joe Giella, And Lettered By Gaspar Saladino)
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In "The Secret of the Golden Thunderbolts," Telle-Teg confronted Hal Jordan. A being from the antimatter universe, Telle-Teg explained he was from the planet Qward, where evil behavior was lawful and good behavior was punished. He warned Hal that the Qwardians had learned how to travel to the positive matter universe of Earth One and begged Hal to warn Green Lantern.
This antimatter universe would come into play in Crisis On Infinite Earths. Also, the Qwardians would arm Sinestro and his fear-powered Sinestro Corps with yellow power rings in "The Sinestro Corps War" story in Green Lantern.
8 Superman Changes History And Splinters The Timeline (July, 1961)
Superman (Vol 1) #146, Written By Otto Binder, And Penciled/Inked By Al Plastino
In "Superman's Greatest Feats!" from July 1961, Superman traveled throughout history, preventing several disasters and saving multiple important historical figures. He prevented the sinking of Atlantis and saved President Abraham Lincoln from being assassinated. Having changed history, Superman resolved to save the population of Krypton.
Superman raced to his home planet ahead of its destruction and built a fleet of starships to shepherd its population to safety. When he saw his infant self being cradled by his mother, Lara, Superman realized he has created a paradox. As he later told Lois when he returned to Earth One, these altered events would continue but in their own separate universes.
7 The Flash Races To Meet The Flash On Earth Two (September, 1961)
The Flash (Vol 1) #123, Written By Gardner Fox, Penciled By Carmine Infantino, Inked By Joe Giella, Colored By Carl Gafford, And Lettered By Gaspar Saladino
During a charity event hosted by Barry Allen's girlfriend Iris West, the Flash inadvertently vibrated at a frequency that transported him to Earth-Two. There, he met Jay Garrick, that world's Flash. Barry, who knew Garrick as a fictional comic book character in his home universe, learned that Jay was on the verge of retiring.
Before Jay could hang up his wings, he and Barry were forced to foil a string of robberies perpetrated by the Thinker. Afterward, Jay resolved to continue his superhero career on Earth-Two, and Barry returned home to Earth-One. The success of "The Flash Of Two Worlds" spawned DC's continued fascination with the multiverse.
6 The Justice League And The Justice Society Cross Paths For The First Time (August, 1963)
Justice League Of America (Vol 1) # 21, Written By Gardner Fox, Penciled By Mike Sekowsky, Inked By Bernard Sachs, Lettered By Gaspar Saladino)
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The trilogy of multiverse adventures for the Justice League began with the first "Crisis" story in DC history. "Crisis On Earth One" saw three Justice League villains from Earth-One (the then-present day DCU) pooling their efforts while, simultaneously, three Justice Society foes from Earth-Two were doing the same.
The two groups of villains communicated and swapped places, forcing their heroic adversaries to face unfamiliar foes. Eventually, the Justice Society crossed over to Earth-One to team up with the Justice League, and both groups pledged to take down the newly formed "Crime Champions."
5 Despero Splits The Justice League Across Three Universes (March, 1964)
Justice League Of America (Vol 1) #26, Written By Gardner Fox, Penciled By Mike Sekowsky, And Inked By Bernard Sachs
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In Justice League of America (Vol 1) #26, Despero transported the Justice League across three separate universes, hoping to divide and conquering. Flash was sent to a universe where the dinosaurs survived and evolved into intelligent, sentient beings. Green Lantern and Batman faced an Earth populated by intelligent inspects.
Meanwhile, Aquaman and Martian Manhunter visited an Earth ruled entirely by intelligent sea creatures. Thankfully, back at Justice League headquarters, Wonder Woman discerned that a rapidly aging Superman was really Despero in disguise. She used the Lasso of Truth to force the confession out of the villain, and Despero returned the Justice League to their home universe.
4 The Crime Syndicate Of America Infiltrates Earth One (August, 1964)
Justice League Of America (Vol 1) #29, Written By Gardner Fox, Penciled By Mike Sekowsky, Inked By Bernard Sachs, And Letters By Gaspar Saladino
The 29th Justice League of America issue marked the first appearance of the Crime Syndicate of America, evil doppelgangers of the JLA from the mirror universe of Earth-Three. "Crisis On Earth-Three" pitted the Justice League against Ultraman (the evil double of Superman), Owlman (Batman), Superwoman (Wonder Woman), and the rest of the Crime Syndicate.
These evil, mirror versions of the Justice League became prominent again during the New 52 era in DC Comics and continued to be among the Justice League's most iconic villains. While it was hardly the first "evil double" story to be done in superhero comics, it was the first-time readers got to see villainous versions who shared similar personalities with favorite heroes.
3 Jimmy Olsen Becomes The Superman-Batman Of Earth-X (June, 1969)
Superman's Pal Jimmy Olsen (Vol. 1) #93, Written By Bill Finger, And Penciled/Inked By Pete Costanza
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Jimmy Olsen, Superman's pal and Daily Planet coworker, found himself transported to an alternate dimension due to a lab accident caused by Professor Potter. When Jimmy arrived in this unfamiliar new universe, he realized he had superpowers.
In the 1969 story, Jimmy first adopted the guise of Superman-Batman, hastily arranging a mismatch of his two favorite heroes' costumes. Later, the Clark Kent of Earth-X dubs Jimmy as Steel-Man. As it turned out, that Clark was the secret leader a criminal League and tried to steal Jimmy's powers before Professor Potter could bring the young photographer home.
2 Crossing Universes Cured Supergirl Of Her Werewolf Dilemma (December, 1969)
Adventure Comics (Vol. 1) #387, Written By E. Nelson Bridwell, And Penciled/Inked By Mort Weisinger
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An attempt to cure Supergirl of her weakness to Kryptonite went awry in Adventure Comics (Vol. 1) #387. The anti-Kryptonite serum developed by the brilliant Dr. Sanford left Supergirl with a hairy, wolf-like face. While Sanford tried to reverse the effects, an explosion during a space launch broke the barrier between universes.
Supergirl met her counterpart from another parallel Earth. There, everyone has hairy, wolf-like faces, and Dr. Sanford's serum caused that Supergirl to have a smooth, hairless face. The two Dr. Sanfords swapped their respective antidotes, and each Supergirl returned to their usual appearances.
1 A Shazam Knock-Off Crossed Paths With Earth-One (June, 1974)
Superman (Vol. 1) #276, Written By Elliott S. Magin, Penciled By Curt Swan, And Inked By Bob Oksner
The original Captain Marvel, known to today's readers as Shazam, was published by Fawcett Comics beginning in 1940. By the time Superman (Vol. 1) #276 dropped in 1974, Marvel Comics owned and was using the name "Captain Marvel." In order to have Superman encounter Captain Marvel, DC needed to get creative.
DC Comics created "Captain Thunder." Young Billy Fawcett was mysteriously transported from his own universe to DC's Earth-One universe. He uttered his magic word "Thunder" and became the mighty Captain Thunder. In his super-powered identity, Thunder tangled with the Man of Steel before the two superheroes teamed up to fight a common enemy.