Who Is The First Avenger? all over time question got an answer
Why was Captain America called The First Avenger, when Hulk and Iron Man were enlisted by Nick Fury before him?
Or are the times between the Hulk & Iron Man movies meant to have taken place after Captain America's return?
This is a case of marketing hyperbole and careful parsing of the facts. Captain America precedes the existence, as a character of both Iron Man and Thor, in fact, he precedes the existence of all of the Avengers being one of the first and most successful of the Avenger's properties. Yes, technically the Avengers formed and THEN they found Cap but in our real world, Captain America appeared first in print.
Captain America is a fictional character, a superhero who appears in comic books published by Marvel Comics. The character first appeared in Captain America Comics #1 (cover-dated March 1941), from Marvel Comics' 1940s predecessor, Timely Comics, and was created by Joe Simon and Jack Kirby.
Thor first appeared in Journey into Mystery #83 (Aug. 1962) and was created by editor-plotter Stan Lee, scripter Larry Lieber, and penciller Jack Kirby. The mythological Thor had appeared previously in Venus #12-13 (Feb-Apr 1951).
Iron Man is a fictional character, a superhero who appears in comic books published by Marvel Comics. The character was created by writer-editor Stan Lee, developed by scripter Larry Lieber, and designed by artists Don Heck and Jack Kirby. He made his first appearance in Tales of Suspense #39 (March 1963).
The Avengers is a team of superheroes, appearing in comic books published by Marvel Comics. The team made its debut in The Avengers #1 (Sept. 1963), and was created by writer-editor Stan Lee and artist/co-plotter Jack Kirby, following the trend of super-hero teams after the success of DC Comics' Justice League of America.