Bucky Barnes is no goofy Robin character, though. Young James "Bucky" Buchanan Barnes was an orphan, the son of a soldier killed during a training exercise. He kept hanging around U.S. Army Camp Lehigh until he was adopted as a sort of mascot, and was even given a uniform, although he was too young to enlist just yet. He befriends Private Steve Rogers, discovers he's the Captain America that he eagerly reads about, and demands to accompany him on missions. The military says "What great propaganda!" and happily ships off this young teenager alongside Cap. This ends up having tragic consequences. The loss of Bucky is why no one else in the Marvel Universe digs adopting teenage sidekicks. Of course, as no one ever stays dead, Bucky eventually came back as the Winter Soldier, a Soviet operative. But again, no one stays on the wrong side in the Marvel Universe for very long.
Marvel won't confirm whether Stan will ever get to play the Winter Soldier, but as he's signed for multiple films and we have a Black Widow running around, I think it's a safe bet. But that is a long, long way off. For now, Cap and Bucky will be fighting the good fight in WWII Europe, and trying to defeat the Red Skull. Let's see how they handle that first.