He was one of the double agents for Hydra, pretending to be loyal to S.H.I.E.L.D., acting as commander of the S.T.R.I.K.E. unit. In the aftermath of the Hydra uprising, he was defeated and left terribly burned. He managed to escape his hospitalization and worked as an independent terrorist, under the codename: Crossbones. He went to Lagos, taking on the Avengers. When he couldn't win, he set off his suicide vest, which was contained by Wanda Maximoff (Scarlet Witch)'s powers.
- Captain America: The Winter Soldier (2014)
- Captain America: Civil War (2016)
- Avengers: Endgame (2019)
- Avengers: Age of Ultron Prelude: This Scepter'd Isle (2015, cameo)
- There are some similarities between Rumlow and Grant Ward, one of the main characters of Agents of S.H.I.E.L.D., who also revealed he was a double agent during the Hydra uprising, although there was more emotional conflict between Ward's choosing, opposed to Rumlow, who seemed pretty certain of his choice.