Sebastian Stan (born August 13, 1983) is a Romanian-born American-raised actor who is best known for his television roles as Carter Baizen on The CW teen drama series Gossip Girl from 2007 to 2010, Jonathan "Jack" Benjamin on the NBC serial drama series Kings in 2009, and portrayed Jefferson/Mad Hatter on the ABC's fantasy drama Once Upon a Time in 2012. He also starred as Thomas "T.J." Hammond on the USA Network drama miniseries Political Animals in 2012.

He played James "Bucky" Barnes/The Winter Soldier in the 2011 film Captain America: The First Avenger, based on the Marvel Comics character. Stan reprised the role in the 2014 sequel Captain America: The Winter Soldier and Ant-Man, and in the 2016 sequel Captain America: Civil War, and will reprise his role in Avengers: Infinity War.