The Avengers (q.v.) is a team of comic book superheroes in the Marvel Comics universe. Over the years it has featured a large number of characters in a variety of combinations.
All of these members helped form the team in The Avengers vol 1 #1 (September, 1963).
A group of superheroes from the 31st century, the Guardians of the Galaxy time traveled to the 20th century in vol 1 #168 (February 1978) and served as honorary members during the Korvac saga.
A group of second-string heroes who independently formed their own branch of Avengers in West Coast Avengers vol 2 #46 (July 1989). Later known as the Lightning Rods.
What If? vol 1, #9 (June 1978) revealed that a prototype group of Avengers had been formed in 1958 to rescue abducted President Eisenhower from supervillain Yellow Claw. They disbanded upon completing their mission but the issue discussed what would have happened had they continued their activities. They were revealed in Avengers Forever to be a parallel world version of the Avengers.
Their members included: