Bucky Barnes/The Winter Soldier
The childhood friend of Steve Rogers/Captain America, Bucky Barnes (Sebastian Stan) has been the catalyst for most of the action within the Captain America franchise. As such, it comes as no surprise that this influence continues to be felt throughout the Civil War conflict.
In Captain America: The First Avenger, Cap was partly motivated by the apparent tragic death of Bucky during a wartime battle. In Captain America: The Winter Soldier, Bucky is revealed to be the titular bad guy, thanks to some Hydra jiggery-pokery.
In Captain America: Civil War, then, Bucky Barnes is once again on board – but this time, Cap appears to have saved him from the clutches of Hydra, and is attempting to protect him from the full might of S.H.I.E.L.D., which undoubtedly has some follow-up questions after Barnes, as The Winter Soldier, went on a rampage through an American city. Cap remains fiercely loyal to his childhood buddy, and it can probably be assumed that this adds to his distrust of authority, and his absolute refusal to acquiesce to demands for greater oversight.
For his part, Bucky Barnes will surely fight on the side of Captain America – because, in doing so, he is also fighting for himself and his own freedom. Whether this is the sum total of his motivations, and whether he is entirely clear of the influence of Hydra, is another question entirely.
