Winter Soldier (Marvel Cinematic Universe)

James Buchanan "Bucky" Barnes, later known as the Winter Soldier, is a character in the Marvel Cinematic Universe, who appears as a tritagonist in Captain America: The First Avenger, and later secondary villain of ''Captain America: The Winter Soldier. He also appears as a protagonist in Captain America: Civil War.''

Initially a close friend of Captain America, Barnes seemingly died during in World War 2. Although presumed dead, Bucky's body was in truth found by HYDRA who brainwashed him into becoming the Winter Soldier, a deadly assassin under HYDRA's control. Despite HYDRA's influence over the Winter Solider, Captain America manages to reach through to Bucky during HYDRA's attack on Washington. Now aware that he is more than just a HYDRA assassin, Bucky flees from Washington. Months later, Helmut Zemo uses the controversy surrounding the Winter Soldier (realaved that he murdered Howard and Maria Stark) to drive the Avengers apart, resulting in a battle between fractions led by Captain America and Tony Stark. Eventually, Bucky decides that it is best for him to return to cryo-sleep until his identity can be fully restored and is frozen in Wakanda.

The Winter Soldier is portrayed by Sebastian Stan.

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, better known as the 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. The 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 the 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.

Ant Man
In spite of his redemption by saving his old friend Steve, Bucky decided to go on the run from the government out of guilt for his crime when he was evil due to Pierce’s brainwashing. However, Sam Wilson and Steve managed to track him down in a remote location. At first, he decided to resist, but they anticipating this by trapping his cybernetic arm in a vice, making him defenseless and unable to fight. When realizing that Steve also comes along to hunt him, Bucky decided to accept his defeat. Steve then ask Barnes whether he knew who he was; Barnes replied that Steve's mother was Sarah Rogers. Rogers and Wilson discussed recruiting him, noting that they would not inform Tony Stark of Barnes' capture and that Wilson knew a guy who could assist them.