James Buchanan "Bucky" Barnes is the sidekick of Captain America, when Bucky accidently walked into Steve's changing room he became Bucky. Bucky was also Captain America when he thinks Steve Rogers is dead. Bucky appeared in Captain America: The First Avenger as a young private, Captain America tried to save him but he fell to his death. After being brainwashed by the Red Skull, he became an agent known as the Winter Soldier but later broke free and became a freelance mercenary.
Bucky wears the same costume based from the comics but trimmed. He wears the usual Winter Soldier in the present day but also trimmed.
Bucky is similar to Batman's sidekick Robin.