Crossbones

Brock Rumlow came out of Hell's Kitchen as a street enforcer, trained under Taskmaster, and found his calling as the Red Skull's personal muscle. Crossbones has no powers, no ideology and no interest in leading anything. What he has is exceptional physical conditioning, mercenary discipline, and a willingness to do the specific violent thing his employer will not say out loud.

His most consequential act was pulling the trigger that started The Death of Captain America. Crossbones fired the shot that put Steve Rogers down at the end of Civil War, though the killing blow came from a mind-controlled Sharon Carter. Frank Grillo's screen version got a similar upgrade in importance, going from Winter Soldier henchman to the suicide bomber whose attack triggers the Sokovia Accords.

Mark Gruenwald and Kieron Dwyer introduced Crossbones in Captain America #359, with a full appearance the following issue, as the newest member of the Red Skull's Skeleton Crew. He became the Skull's most reliable operative and, alongside Sin, part of the closest thing that organisation has to a family.

Ed Brubaker's run gave him his defining role: Crossbones fired the shot that felled Steve Rogers in Captain America #25, opening The Death of Captain America, one of Marvel's best-selling storylines of the 2000s. He has since cycled through Thunderbolts rosters and Hydra operations, always as the hired hand nobody trusts and everybody uses.