Sharon Carter, alias Agent 13, is a fictional character, a secret agent in the Marvel Comics universe. She is an ex-field agent of S.H.I.E.L.D. under Nick Fury and the girlfriend of Captain America.
In original comic book continuity, Sharon was said to be the younger sister of Peggy Carter, the wartime love interest of Captain America, but she was later retconned as Peggy's niece because of the unaging nature of comic book characters. She was portrayed by Emily VanCamp in the film Captain America: The Winter Soldier. ...more on Wikipedia