Winter Soldier (Marvel Cinematic Universe)

James Buchanan "Bucky" Barnes, later known as the Winter Soldier, is a character in the Marvel Cinematic Universe. He is a tritagonist in Captain America: The First Avenger and the secondary title antagonist in Captain America: The Winter Soldier. He was supposed to be the main antagonist of the film, but this was part a misinformation campaign to hide the true main villain of the film.

Captain America: The First Avenger
Bucky is first seen in the film as a sergeant in the US Army. He sees Steve being beat up by a bully and comforts him after a brief confrontation. He takes Steve and two girls to a World of Tomorrow Exhibit and departs to be deployed. He is next seen where he is being held captive by HYDRA and stripped to a chair. Captain America rescues him, only to find himself meeting Johann Schmidt (Red Skull). Afterwards, Captain America recruits him as his second-in-command of the Howling Commandos team to square off against Red Skull's HYDRA henchmen and destroy every HYDRA base in the overseas area. He is last seen in this film when Captain America and his team are deployed to bring HYDRA scientist Arnim Zola into custody. When a HYDRA  goon fires at Bucky with the Captain's shield, he instead is sent on the side of the train. Before Captain America could save Bucky, he falls to his apparent death into an icy cold riverside.

Captain America: The Winter Soldier
In between Captain America: The First Avenger and The Avengers, Bucky was found by HYDRA and brainwashed by Alexander Pierce to being an assassin operative of HYDRA as The Winter Soldier. He is first seen when Nick Fury was being chased by rogue policemen sent by Pierce to kill him. He shot a grenade at Fury's car and made it fly into the air. He then follows Fury to Captain America's apartment and severely wounds him. Captain America throws his shield at the Winter Soldier, but he reflects it and throws it back at Captain America.

Black Widow reveals that she had a recent encounter with the Winter Soldier and unveils that he is a ghost to most of society. He is next shown when he is sent to Alexander Pierce's home to receive his next assignment. Pierce tells him that his next targets were to be Captain America and Black Widow, who were attempting to discover Pierce's plan to use the SHIELD Helicarriers and target over a million people.

Afterwards, he attacks Rogers, Romanoff and Sam Wilson, who were driving while proceeding with their investigation of Jasper Sitwell and the revelation of HYDRA's plan. After he kills Sitwell, the Winter Soldier tries to fire a missile at Rogers and Romanoff, but Rogers deflects it and it ends up destroying a bus. While engaging Black Widow, the Winter Soldier pursues her through the streets of Washington DC before coming across Rogers. After a one-on-one duel, Rogers rips off his mask and discovers that the Winter Soldier is actually Bucky. Before he could raise his gun, Bucky was knocked to the ground by Sam Wilson.

Back at the lair, the Winter Soldier starts to remember his past while trying to give Alexander Pierce a full report on his mission. Pierce then puts him into another brainwashing treatment making him forget everything from his past life, though this time, the brainwash effect not last long. During the climax, Winter Soldier fought Captain America, but the Helicarrier where they fought, along with everyone on board crashes.

Eventually, the brainwash effect upon the Winter Soldier wore off. Regaining his senses, he rescues Captain America from drowning, before disappearing and takes Pierce with him. In a post-credits scene, the Winter Soldier visits the Captain America exhibit at the Smithsonian Institution to learn of his past, hints a sign of possible redemption; with his memory back and the brainwash effect wore off, he is likely less evil in the end and he likely wanted to meet his old friend.