Crossbone

Crossbones, whose real name is Brock Rumlow, is a supervillain in Marvel Comics and one of Captain America's most notable adversaries. He first appeared in Captain America #359 (October 1989). Crossbones is a ruthless mercenary and assassin, often employed by villains such as Red Skull and Hydra. He was once the leader of a New York street gang before training at Taskmaster’s school for criminals, becoming an expert in various fighting styles, military tactics, and weaponry. Crossbones is recognized by his signature black-and-white skull mask and crossbones insignia on his chest. In comics, he has participated in numerous battles against Captain America and was involved in the assassination attempt on Captain America after the Civil War event. Crossbones also briefly joined Luke Cage's Thunderbolts team and gained energy blast abilities, which he soon lost. In the Marvel Cinematic Universe, Crossbones is portrayed by Frank Grillo, initially appearing as a S.H.I.E.L.D. agent before being revealed as a Hydra operative, engaging in multiple conflicts with Captain America. He is a frequent presence in the Marvel universe, causing significant trouble for superheroes.