July 22's Captain America: The First Avenger; his shield appeared in the background of a scene in 2008's Iron Man; and his frozen body was reportedly in a deleted scene of The Incredible Hulk
In 1942, skinny Steve Rogers joins Project Rebirth so he can fight in World War II. The experiment works and Rogers becomes the super soldier Captain America, who fights Nazis, the organization Hydra, and Johann Schmidt, aka the Red Skull (Hugo Weaving), who plans for world domination with the help of the Cosmic Cube, a powerful Tesseract.
Much like the comics, it seems Captain America will be frozen in suspended animation inside a block of ice and thawed when he's discovered by the Avengers (as depicted in 1964's The Avengers #4). With recent spy photos revealing Evans shooting a scene alongside Nick Fury (Samuel L. Jackson) in modern-day New York, it appears Cap's placement in the present won't be limited to The Avengers.
In the comics, Captain America eventually becomes the leader, despite joining the team in the fourth issue. However, Iron Man has been the character with the longest involvement in the Avengers Initiative, making him the more natural choice for Avengers leader in Marvel's "Cinematic Universe." Whedon has said that there won't be any tension between Iron and Cap like in Marvel's infamous "Civil War" storyline (which saw the two heroes on opposite ideological sides), with "witty banter" being the vehicle that eases any conflict. Evans recently admitted that there is "this kind of friction between myself and Tony Stark" in the movie.
Also, since The Avengers is the first movie (chronologically speaking) to show Cap in the present, expect Cap to be still unfamiliar with his surroundings. Evans recently admitted that the appeal of playing Cap in The Avengers was playing a character with some "meat on the bone," adding: "If you woke up one day and it was 50, 60 years in the future and everyone you knew had passed away and the entire world around you is different — that'd be a lot to take in." Evans has admitted that the Avengers script makes use of Cap's "fish out of water" situation, and that his new time period will also include the addition of a new costume.
Marvel president of production Kevin Feige recently told Collider that the first scene shot for The Avengers involved Evans and Jackson. However, Feige said, "That doesn't mean that is the beginning of the movie and that doesn't mean that is the Times Square scene, but they were first up."
Not much beyond the recent MTV interview, but Evans did admit he's "trying to get big again" to play the role.