James Buchanan Barnes was the son of a soldier killed in training at Camp Lehigh in Virginia shortly before the United States entered the Second World War. He is a lone teenager without a father but is quickly adopted by the camp and nicknamed “Bucky” by the soldiers. He becomes good friends with one of the soldiers, a private by the name of Steve Rogers. One day he catches Rogers changing his uniform, from that of a soldier, into that of the mysterious superhero, Captain America.
Bucky insists on joining Cap on his adventures fighting the Nazis and is put through extensive training to become Cap’s partner and sidekick. The military justifies this by using Bucky as a symbol to other teenage boys to rally the youth of America in support of the war effort.
Bucky fights alongside Cap as a duo and as part of the superhero team, The Invaders. He also helps organize a young superhero team call the Liberty Legion as well as another one called Kid Commandos.
Toward the end of the war, Captain America and Bucky try to stop an experimental drone plane that has been launched by Baron Zemo with explosives on board. The plane explodes, casting Captain America into the frozen Arctic and killing Bucky who stayed on board still trying to defuse the explosives. Decades later, Captain America is found by the Avengers and revived. He then goes on for many years, mourning the death of his young friend and blaming himself.
Bucky of course is revived and becomes the International Assassin known as the Winter Soldier.