The Avengers is a team of fictional superhero characters in comic books published by Marvel Comics. Originally created using preexisting Marvel characters, variously created by writer-editor Stan Lee, artist and co-plotter Jack Kirby and others, the team first appeared in The Avengers #1 (Sept. 1963).
Labeled "Earth's Mightiest Heroes", the Avengers originally consisted of Ant-Man, Wasp, Thor, Iron Man, and the Hulk. Almost from inception, however, the roster has been fluid: The Hulk departs; Captain America joins and soon afterwards leads a whole new team. The rotating roster has become a hallmark of the team, although one theme remains consistent: the Avengers fight the foes no single superhero can withstand — hence their battle cry, "Avengers Assemble!" The team has featured humans, robots, gods, aliens, supernatural beings, and even former villains.(Wikipedia)