In the Marvel 'Avengers' films, who played the Winter Soldier?

"Captain America: The Winter Soldier" is a 2014 American superhero film based on the Marvel Comics character Captain America, produced by Marvel Studios and distributed by Walt Disney Studios Motion Pictures. It is the sequel to "Captain America: The First Avenger" (2011) and the ninth film in the Marvel Cinematic Universe (MCU). In the film, Captain America (Chris Evans) joins forces with Black Widow (Scarlett Johansson) and Falcon (Mackie) to uncover a conspiracy within the spy agency S.H.I.E.L.D. (Supreme Headquarters, International Espionage and Law-Enforcement Division) while facing a mysterious assassin known as the Winter Soldier (Sebastian Stan).

James Buchanan "Bucky" Barnes (Winter Soldier) is Captain Americas' childhood best friend who has re-emerged as an enhanced brainwashed assassin after supposedly being killed in action during World War II.

Stan endured five months of physical training to prepare for the role and did historical research, stating, "I dove into the whole Cold War thing. I looked at the KGB. I looked at all kinds of spy movies, and all kinds of documentaries about that time, and what it was about. I grabbed anything from that time period. Anything about brainwashing."