In 1997, Marvel Comics and DC Comics collaborated to bring their universes together for a comic book miniseries alternately referred to as "Marvel vs. DC" and "DC vs. Marvel." It was not the first time, as Superman and Spider-Man had teamed up in the 1970s.
Marvel vs. DC, DC vs. Marvel
The two comic universes came together when the incarnations of their respective universes (referred to as "the Brothers") became aware of each other after aeons of slumber. To prevent the Brothers from destroying each other, characters from each universe battled to determine which universe would survive; several of the matches were determined by online voting.
When the fights concluded (including controversial victories by Wolverine and Storm over Lobo and Wonder Woman, respectively), neither universe was willing to go. To prevent total destruction, the Spectre and the Living Tribunal created a merged universe.
Amalgam Comics
For two months, Marvel and DC published "Amalgam Comics," a universe where their characters were merged (Captain America + Superman = Super-Soldier; Wolverine + Batman = Dark Claw; Doctor Doom + Doomsday = Doctor Doomsday; Lobo + Howard the Duck = Lobo the Duck)), ((Justice League + X-men = Justice League X)) and only Axel Asher and Dr. Strangefate (Doctor Strange + Doctor Fate + Professor X) knew the truth, and struggling against each other to reverse or preserve the change.
During the publication of Amalgam Comics, the companies treated it as if it had always existed, giving it a fictional history stretching back to the Golden Age of Comics, as well as retcons and reboots, such as the Secret Crisis of the Infinity Hour (Secret War + Crisis on Infinite Earths + Infinity Gauntlet + Zero Hour), including an Amalgam version of the cover of CoIE #7, with Super-Soldier holding his sidekick's body.
Eventually, Axel Asher (now "Access") managed to separate the Brothers with the help of Amalgam's heroes, and all went back to normal.
