Who Is He: Brock Rumlow is the only villain on this list who has already appeared in the MCU. He does not have any superpowers, but his physique and fighting skills are second to none.As an ardent HYDRA supporter and hitman, Crossbones proved himself a dangerous foe in Captain America: The Winter Soldier. How He Could Fit Into The Show: Not being a big enough name to be the primary villain of a Marvel film, he could be a recurring threat to S.H.I.E.L.D. as they continue battle HYDRA throughout the series. Having been badly burned by a crashing Helicarrier, he could don his classic skull mask and continue his personal (or HYDRA sanctioned) vendetta against S.H.I.E.L.D.