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), and Avengers: Endgame (2019). Additionally, Grillo voices alternative versions in the Disney+ animated series What If...? (2021). Publication history Created by writer Mark Gruenwald and artist Kieron Dwyer, Crossbones first made a cameo appearance in Captain America #359 (October 1989) as a shrouded figure watching from the shadows, making a full appearance during the "Bloodstone Hunt" storyline in issue #362. He has appeared as a regular character in Thunderbolts beginning with issue #144, but was dismissed from the team in issue #151. Fictional character biography Brock Rumlow led the Savage Crims gang on New York City's Lower East Side, during which time, he assaulted fifteen-year-old Rachel Leighton and fought Rachel's two brothers, killing the elder brother. Rumlow fled, entering Taskmaster's school for criminals, within three years becoming an instructor under the name Bingo Brock. As a mercenary, Rumlow enlisted with Albert Malik, the communist Red Skull, in Algeria, serving the Red Skull under the name Frag until he was sent to invade Arnim Zola's Switzerland chateau; Rumlow was ultimately the only team member to survive the assault. There, he also met and impressed, Johann Schmidt, the original Nazi Red Skull, who accepted Brock's services and code-named him as "Crossbones". The true Red Skull sent Crossbones to observe Baron Helmut Zemo's progress acquiring the Bloodstone fragments and to obtain them. He stowed aboard Captain America's flagship, and entered Zemo's ship to steal the Bloodstone fragments. He overpowered Diamondback, and shot a crossbow bolt that coupled with Captain America's shield. Crossbones was forced to shatter the Bloodstone fragments when the alien entity known as the Hellfire Helix used it to take control of Baron Heinrich Zemo's body; the destruction of the Bloodstone discorporated the Hellfire Helix. Knowing that his master would be infuriated by the Bloodstone's loss, Crossbones kidnapped Diamondback to Madripoor as bait for Captain America. He challenged Captain America to retrieve Diamondback, but the Captain defeated him, although Diamondback escaped, and the Red Skull ordered Crossbones to desist and return to headquarters. The