First Appearance: Captain America Comics #1 (March, 1941).
Golden Age Appearances: Captain America Comics #1-74, All Winners Comics v1 #1-19, 21, Young Allies #1-5, USA Comics #6-17, All-Select Comics #1-10, Marvel Mystery Comics #80-84, 86-92, Blonde Phantom #16, All-Winners Comics v2 #1, Human Torch #33, 35, Sub-Mariner #31.
Modern Appearances: Too many to count (have mercy on a poor annotator!)
Dates Active: 1941-1945, twelve years ago to the present.
Steve Rogers, a frail and sickly young man, was enspired to enlist in the Army out of his sense of patriotism and his loathing for what the Nazis were doing in Europe. He was rejected because of his poor health, but after pleading to be accepted into the Army he was offered the chance to be a part of a special experiment. He accepted, of course. He was tested and then injected with a Super-Soldier serum and exposed to "vita-rays," the combination of which made him into a perfect human specimen. After extensive training, he put on a costume, called himself Captain America, and went out to fight crime and the Axis. He quickly acquired a sidekick, Bucky (I), and had a long list of adventures kicking Axis butt. In 1948 Bucky was rendered hors de combat, and Captain America gained a new sidekick, the Golden Girl (I). In the 1950s Cap and Bucky briefly returned, but disappeared as soon as their book folded.
Then, during the Silver Age, Captain America returned, and his continuity was revised. During the war he'd been a part of the superteam the Invaders. In 1945, late in the war, he and Bucky went after the Nazi Baron Zemo; Zemo launched a bomb-laden drone-plane at London, and when Bucky and Cap tried to stop it, the plane exploded, killing Bucky and throwing Captain America into the icy ocean waters. Cap was sent into suspended animation, and was found and defrosted years later. Since then he has served with distinction on the Avengers.
Captain America has no superpowers, but (depending on the day of the week and the whim of the writer) has the Super-Soldier serum in his veins and has his shield. Plus his fighting skills, of course.
Useful Captain America Site
Star-Spangled Site. Dave Medinnus' excellent site on Cap.