James Barnes, also known as the Winter Soldier, is a key character in the Captain America series within the Marvel universe. Once Steve Rogers' best friend, Barnes is presumed dead during World War II but is later revealed to have survived, brainwashed as an assassin by Hydra. His journey is marked by internal struggle, redemption, and loyalty, as he strives to regain his lost identity and atone for his actions while under Hydra's control. His complex relationship with Captain America is central to the series.