During the dark days of the early 1940's, a covert U.S. Military experiment turned Steve Rogers into America's first Super-Soldier, Captain America. Throughout the war, Cap and his partner, Bucky fought alongside infantry and with a group of heroes known as the Invaders. In the closing months of World War II, Captain America and Bucky were both presumed dead in an explosion. Decades later, Captain America was found trapped in ice and revived in the modern world. Captain America would then later go on to be one of the most important members of the Avengers as well as a leader of the team.
As a symbol of freedom and patriotism, a number of men have taken the mantle of Captain America in Rogers' various absences. Of note are William Nasland and Jeffrey Mace, Bucky Barnes, and Sam Wilson.