The titular team debuted in Avengers #1 (in September 1963), using existing characters created primarily by writer-editor Stan Lee with penciler and co-plotter Jack Kirby. Labeled « Earth's Mightiest Heroes », the Avengers originally consisted of Ant-Man (Hank Pym), Wasp (Janet Van Dyne), Thor, Iron Man (Tony Stark) and the Hulk (at a time when the Hulk was more intelligent). The original Captain America was discovered by the team in Avengers #4, trapped in ice, and he joined the group when they revived him. The rotating roster has become a hallmark of the team, although one theme remains consistent : the Avengers fight « the foes no single super-hero can withstand ». The team is famous for its battle cry « Avengers Assemble ! ».

The next milestone came when every member but Captain America resigned and were replaced by 3 former villains : Hawkeye, the Scarlet Witch and Quicksilver. Although lacking the raw power of the original team, the quartet proved their worth by fighting and defeating the Swordsman, the original Power Man and Doctor Doom. They are soon rejoined by Hank Pym (who changes his name to Goliath) and the Wasp, along with Hercules, the Black Knight and the Black Widow, although the last 2 do not obtain official membership status until years later.

When writer Roy Thomas commenced, there was a greater focus on characterization. The Black Panther joins the team, followed by the Vision. Roy Thomas also established that the Avengers are headquartered in a New York City building called Avengers Mansion, provided courtesy of Tony Stark who also funds the Avengers through the Maria Stark Foundation, a non-profit organization. The mansion is serviced by Edwin Jarvis, the Avengers' faithful butler, and also furnished with state-of-the-art technology and defense systems, including the Avengers' primary mode of transport : the 5-engine Quinjets. The adventures increased in scope as the team cross into an alternate dimension to battle the Squadron Supreme and fight in the Kree-Skrull War, an epic battle between the alien Kree and Skrull races and guest-starring the Kree hero Captain Marvel.