Old Skull is from Earth-691, an alternate earth where an Martians attacked the earth and won. Old Skull was genetically transformed into gladiators and forced to battle other humans.
Old Skull escaped and joined the Freedom Fighters, and rebeled against the aliens.
During Marvel Zombies Old Skull was biten and Killraven had to cut off his arm before the virus turned Old Skull into a zombie himself.
Above average unarmed fighter.