Crossbones (Brock Rumlow) is a supervillain appearing in American comic books published by Marvel Comics. The character is usually depicted as an adversary of Captain America, and played a part in his assassination. The character has been adapted into multiple forms of media, most notably being portrayed by Frank Grillo in the Marvel Cinematic Universe films Captain America: The Winter Soldier (2014), Captain America: Civil War (2016), Avengers: Endgame (2019). Additionally, Grillo voices alternative versions in the Disney+ animated series What If...? (2021).