"Crossbones" is a fictional character appearing in Marvel Comics. He is often depicted as an antagonist to Captain America and is known for his ruthless nature and combat skills. Crossbones typically wears a skull mask and is associated with various criminal organizations, including Hydra. The character first appeared in Captain America #359 in 1990, created by writer Mark Gruenwald and artist Kieron Dwyer. Crossbones is often portrayed as a mercenary and assassin, skilled in hand-to-hand combat and weaponry. His connections to Red Skull and other villains in the Marvel Universe further establish him as a significant threat to heroes.