Captain America, whose alter ego is Steven "Steve" Rogers, made his debut in Captain America Comics #1, published by Timely Comics (Marvel's predecessor) with a cover date of March 1941, though it went on sale December 20, 1940. Created by Joe Simon and Jack Kirby, the character was introduced as a patriotic super-soldier during World War II, famously depicted on the cover punching Adolf Hitler. A frail young man from Brooklyn rejected by the U.S. Army due to his physical weaknesses, Rogers volunteers for Operation: Rebirth, receiving the experimental Super-Soldier Serum and Vita-Ray treatment that transform him into the peak of human physical potential. Armed with an indestructible shield—initially triangular, soon redesigned as circular—he fights Axis powers alongside his young sidekick Bucky Barnes.

Captain America embodies unwavering moral integrity, selflessness, and a commitment to liberty and justice, serving as a symbol of American ideals during wartime. In his early adventures, he combats Nazi saboteurs, spies, and villains like the Red Skull, often as part of teams such as the Invaders. His stories emphasized propaganda against fascism, contributing to his immense popularity in the 1940s. Following the war, the character's series waned with declining superhero interest, leading to a brief 1950s revival as a "Commie Smasher" before cancellation.

In the Silver Age, Captain America was revitalized in Avengers #4 (March 1964), revealed to have been preserved in suspended animation after a 1945 mission left him frozen in Arctic ice. Thawed by the Avengers, he joins the team as a leader and moral anchor, navigating the complexities of the modern world while grappling with lost time and ideals. Over decades, Rogers has experienced profound developments, including temporary loss of the mantle (e.g., becoming "The Captain" in the 1980s, passing it to associates like Bucky Barnes or Sam Wilson during periods of death, depowerment, or disillusionment), conflicts in events like Civil War, and battles against threats from Hydra to cosmic entities, solidifying his enduring legacy as Marvel's sentinel of liberty.