He serves as one of the most enduring adversaries of Captain America, and even played a part in his assassination in the aftermath of the superhero Civil War.

Young Brock Rumlow led the Savage Crims gang on New York City's Lower East Side.

[4] As a mercenary, Rumlow enlisted with Albert Malik, the communist Red Skull, in Algeria, serving him as Frag until he was sent to invade Arnim Zola's Switzerland chateau.

Ultimately the only team member to survive the assault, Rumlow met and impressed Johann Shmidt, the original Nazi Red Skull, who accepted Brock’s services and codenamed him "Crossbones".

[5] The true Red Skull sent Crossbones to observe Baron Helmut Zemo's progress acquiring the Bloodstone fragments and to obtain them.

[8] Knowing that his employer would be infuriated by the Bloodstone's loss, Crossbones kidnapped Diamondback to Madripoor as bait for Captain America.

[23] Desperate to regain his position as leader of the Skeleton Crew, Crossbones kidnapped Diamondback, imprisoning in an abandoned subway station and forced into a brutal regime of combat training.

[volume & issue needed] Diamondback stole samples of Captain America's blood from the Avengers' mansion, then accompanied Crossbones to the Red Skull's mountain fortress.

[volume & issue needed] He was later attacked by Cutthroat, the Skeleton Crew's new leader, who feared that Crossbones will try to take back his position as the Red Skull's right-hand man.

[volume & issue needed] He was critically wounded by flying shrapnel during an assault on the fortress by Captain America and the Falcon, and imprisoned.

[volume & issue needed] Imprisoned in the Raft when Electro breaks the inmates out, Crossbones was seen fighting Captain America and Spider-Man.

[volume & issue needed] Crossbones and his new lover, Synthia Schmidt (the Red Skull's daughter), began hunting Aleksander Lukin, the Winter Soldier's commander.

[volume & issue needed] While they escape the destruction of the plane, they found Agent 13, and are about to kill Sharon Carter, only to be stopped by the Red Skull's appearance.

[volume & issue needed] While being led from Federal Courthouse, Captain America was shot in the shoulder by Crossbones taking the Red Skull's orders.

[volume & issue needed] In Fallen Son: The Death of Captain America, Wolverine, along with Daredevil and Doctor Strange, broke into S.H.I.E.L.D.

[volume & issue needed] They then capture the Winter Soldier when confronting Lukin to find out a relationship with the Red Skull.

[volume & issue needed] When Sin and the Serpent Squad attacked the Senate Building, Bucky Barnes arrived as the new Captain America.

[volume & issue needed] At the start of the "Heroic Age" event, Crossbones has become a member of the new Thunderbolts team formed in the aftermath of Siege.

[27] Government agents, working with Luke Cage, add Crossbones to the team knowing that he cannot be reformed, hoping that his extreme methods will alienate the other Thunderbolt members and push them towards rehabilitation.

[30] Fearing that the Thunderbolts are close to being disbanded following Cage's decision to leave, Crossbones attempted to escape alongside Ghost and Juggernaut.

[36] Crossbones later appears as a member of Hydra who are planning to spread poisonous blood extracted from an Inhuman boy named Lucas.

[40] During the "Secret Empire" storyline, Crossbones appears as a member of the Army of Evil and took part in the attack on Manhattan in retaliation for what happened at Pleasant Hill.

[volume & issue needed] Physically, Crossbones is tall and well built, but moves with an athletic grace uncommon for a man of his bulk.

[31] An alternate universe variant of Crossbones from a pocket dimension created by Franklin Richards appears in Heroes Reborn as an enforcer for the Red Skull and Master Man's World Party.