Actor Sebastian Stan is an American actor best known for his role as Bucky Barnes in the Marvel Cinematic Universe. He has also appeared in films such as Captain America: The First Avenger, The Martian, and I, Tonya. He is also known for his roles in television series such as Gossip Girl and Once Upon a Time. His full name is Sebastian Stan Cabot, with the last name being the answer to the crossword clue 'Cabot'. His first name is the answer to the crossword clue 'Stan', which is four letters long.