Winter Soldier (Marvel Cinematic Universe)

James Buchanan "Bucky" Barnes, later known as the Winter Soldier, is a villain turned supporting protagonist in the Marvel Cinematic Universe.

Initially a close friend of Captain America, Barnes seemingly died during in World War II. 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 (revealed 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.

He was portrayed by Sebastian Stan.

Captain America: The First Avenger
Bucky is first seen in the film as a sergeant in the US Army and as the tritagonist. 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
He re-appears as the titular secondary antagonist before redeeming himself in this movie.

In between Captain America: The First Avenger and The Avengers, Bucky was found by HYDRA and brainwashed into 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 the intelligence 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 grenade 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.

Between Captain America: Winter Soldier and Ant-Man
But beforehand, he decided to returned to Ideal Federal Savings Bank, where he falsely informed two scientists present that Captain America was dead. As the scientists relaxed momentarily, Barnes attacked and attempted to kill them and began destroying much of the machinery which had been used to control and torture him for so many decades. However, as memories and images of past assassinations for HYDRA raced through his mind, Barnes relented and fled to try and get away from his violent history and learn the truth about his past once and for all.

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.

Captain America: Civil War
In Captain America: Civil War, Bucky returned as one of the main protagonists. Here, it's revealed that after his brainwash into a Winter Soldier by HYDRA, five other soldiers were also brainwashed in the same way into other Winter Soldiers and locked and frozen due to fear that they would rampage and start the riot. HYDRA also revealed to have arranged a fail-safe procedure in his brainwashing process in form of trigger words that would revert Bucky to his brainwashed self for a certain amount of time should he revert to his original good self and turn against them.

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.

Personality
"This doesn't have to end in a fight, Buck. It always ends in a fight."

- Captain America and Bucky Barnes

Bucky Barnes was extremely courageous, resourceful, jingoistic, staunch, dependable, devoted, loyal, sincere, steadfast, refractory, trustworthy, headstrong, and patriotic, so he had a strong moral center. He was a good and close friend to Steve Rogers during their youth; he helped him when he got into fights and tried to cheer him up and look after him when Rogers' mother died. Best friends since childhood, they went through many trials and tribulations together. He was also protective and of Rogers, as when he planned to enlist in the United States Army. Barnes tried to talk him out of it, as he knew he would die because of his physical condition and poor health.

Due to his advanced physiology however, Barnes survived his apparent death, but was found by HYDRA instead. Trained as a living weapon, Barnes became a new man so to speak as his memories and identity were constantly being wiped until he was augmented into the perfect assassin, the Winter Soldier. As the Solider, he was brutal and ruthless with an utter lack of conscience, and followed remorselessly on Hydra's any order. Even so, he still saved Steve Rogers from drowning after the Insight Helicarrier blew up. Although he states he did not know why he did such, it was due to Rogers reminding him of who he was, which he initially reacted with violence before finally accepting.

While he still holds a mostly serious demeanor, he is still shown to retain a sense of humor, as shown when he and Falcon both smiled with approval at Rogers' kiss with Sharon Carter and later as the two reminisced over earlier times in their friendship. His sense of humor can also be dry at times, as shown when he asked Wilson why he couldn't use his gadget on Spider-Man earlier to take him down.

Even though Barnes has regained his identity and former values, he has also developed a guilt-ridden conscience, and became deeply ashamed over his actions as the Winter Soldier. He previously stated that he has an absolute memory of every person he has killed, and knows that the fact he was brainwashed does not change the fact that he killed them. Fearing for his mental state and anyone around him (as Helmut Zemo was able to manipulate him with the Winter Soldier Program), Barnes ultimately decided that placing himself in cryogenic stasis until he can be cured of HYDRA's mental programming completely would be the best course of action.

Powers and Skills

 * Super-Soldier Serum: As a super-soldier, he has all the physical abilities of Captain America, ranging from increased strength, speed, reflexes, stamina, durability, healing, senses, mental faculties and longevity.
 * Cybernetic Arm: His left arm is cybernetic, allowing him higher levels of superhuman strength.
 * Master Combatant: He is a highly skilled martial artist, being one of the best in the world. He is also a professional espionage operative, stealth tactician and sharpshooter.