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Brock Rumlow, portrayed by Frank Grillo, is a character in the Marvel Cinematic Universe (MCU). Initially appearing as a S.H.I.E.L.D. operative in "Captain America: The Winter Soldier," Rumlow later becomes the villainous Crossbones in "Captain America: Civil War." As Crossbones, he aligns himself with Helmut Zemo and participates in the plot to divide the Avengers.