9. The Winter Soldier (Marvel Cinematic Universe)
We've already seen Bucky Barnes in the first Captain America movie - Steve Rogers' good friend seemingly plummeted to his death following an action sequence aboard a fast-moving train - but he will be returning under the guise of the Winter Soldier in the sequel. In the comics, the Winter Soldier is fitted with a cybernatic arm and programmed to be an evil assassin. It will certainly be interesting to see how it is explained that Bucky Barnes survived his fall, but it will be more interesting to see how Captain America reacts to having to fight against his oldest friend. Sebastian Stan is set to reprise the role of Bucky Barnes in the sequel.