The Avengers title began with issue #1, written by Stan Lee and drawn by Jack Kirby. The original Avengers team consisted of characters taken from other books - Thor from Journey Into Mystery, Iron Man from Tales Of Suspense, and the Hulk, Ant Man, and the Wasp from Tales To Astonish. The Hulk lasted only a few issues before becoming an enemy of the team (quickly teaming up with a revived Sub-Mariner).
Issue #4 reintroduced Captain America, the classic World War II hero whose adventures hadn't been published in nearly a decade. The Captain quickly became an important member of the team, especially so after such powerful characters as Thor and Iron Man left the team. For a time Captain America led a new, less substantially powerful group of Avengers, consisting of Giant Man (formerly Ant Man) and the Wasp, as well as former villains Hawkeye, Quicksilver, and the Scarlet Witch.
Over time the Avengers lineup continued to evolve and change. Many of Marvel's second-line characters became Avengers for a time, or at least appeared within the title for an issue or two. The 1970's classic lineup of Captain America, Thor, Iron Man, the Scarlet Witch, the android called the Vision, and others would prove to be the most popular with readers.