James Buchanan "Bucky" Barnes is a fictional superhero appearing in American comic books published by Marvel Comics. Originally introduced as a sidekick to Captain America, the character was created by Joe Simon and Jack Kirby and first appeared in Captain America Comics #1 (cover-dated March 1941) (which was published by Marvel's predecessor) as the original and most well-known incarnation of "Bucky". The character is brought back from supposed death as the brainwashed assassin Winter Soldier and later assumed the role of Captain America when Steve Rogers was presumed to be dead.

IGN listed Bucky Barnes as the 53rd greatest comic book hero of all time stating that (after Robin) Bucky is easily the most iconic superhero sidekick of the Golden Age and describing him as one of the central players in the Marvel Universe since his role of being Captain America. IGN also lists Bucky as #8 in their list of "The Top 50 Avengers" in 2012. Sebastian Stan portrays the character in the Marvel Cinematic Universe starting with the Captain America films and later reprising the role in Avengers: Infinity War and its Untitled sequel.

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