A quarter century in the making, DC and Marvel's two flagship superteams were originally supposed to unite in the early 1980s in a story scripted by Roy Thomas and illustrated by celebrated Superman/Justice League/Avengers artist George Perez, but editorial disputes led to the project being shelved until the early 2000s, despite Perez having already drawn almost a full issue of the story. The completed book was eventually drawn by Perez from a script by then-current Avengers writer Kurt Busiek, and it features pretty much every Avenger and every member of the Justice League of America - not to mention every villain both teams had ever fought up to that point - which is probably about as big as they needed to go for a story they might only get one chance to tell. The story sees both teams introduced by way of a Secret Wars-type game in which they must find objects of power in the others' universe before turning on the being responsible for the 'game' and having both worlds merged with one another, making for an alternate history in which Captain America, Superman, Iron Man and Batman had always been fast friends. It doesn't last, of course, but it certainly makes for some iconic moments including Superman wielding Thor's hammer and Cap leading the heroes from both worlds into battle.
