Brock Rumlov (Earth-6457)

Brock Rumlov was an agent of Hydra acting undercover on Third Echelon as the leader of STRIKE, a tactical counter-terrorism unit of lethal soldiers. When Hydra's operations within the Echelon were revealed, and Project Blacklist was activated, Rumlov attempted to kill Captain America, but was confronted by Falcon, getting badly damaged in a explosion. Hospitalized, he escape, and sought vengeance using the alias of Crossbones.