Karkas was born to the race of Deviants, an evolutionary offshoot of humanity which is cursed with an unstable genetic code causing random characteristics to crop up with every newborn Deviant child. Karkas was far more monstrously mutated than most Deviants, and was labeled a "mutate." The Deviant priesthood publicly marks for execution all Deviants whom it considers to have varied too greatly in their genetic codes from the rest of their race. Some of these extreme cases, however, are raised to fight as gladiators in the arena before they are sent to their final fate. Karkas quickly developed such size and strength that he was selected to become a gladiator. Although his heavily hided body could resist extremes of punishment, Karkas never had any special inclination to become a fighter. Therefore, he did the minimum required of him as a gladiator to permit his continued existence. In fact, Karkas had a great natural sensitivity emotionally, and was a born philosopher, despite the role of a savage monster that he was forced to play.
Eventually Karkas was pitted against another mutate, the human-looking Ransak the Reject, in a gladiatorial combat witnessed by the Deviants' then-monarch Tode, Warlord Kro, and a visitor to Deviant Lemuria, the Eternal known as Thena. Despite Karkas' far greater size and strength, the savage Reject bested him in battle, wounding him terribly. But then the Deviant city began being destroyed by the alien Eson the Celestial. Amid the turmoil, Karkas asked Thena for sanctuary with her, so that he would be saved from eventual death in the arena and could instead spend his life in a more fruitful way. He also asked for sanctuary for the Reject, whom, he pointed out, was not born as a "killing machine" but had been turned into one by the Deviants. Thena felt compassion for both and teleported herself, Karkas, and the Reject to Olympia, her home.
Karkas has remained on Olympia since then, acting as Thena's loyal companion and taking advantage of enlightened cultural opportunities but his current whereabouts are unknown.
Karkas possesses various superhuman attributes apart from his superhuman strength. His thick hide can withstand concussive forces up to those of a small anti-tank missile before sustaining serious injury. His recuperative powers are about twice that of human beings. His speed and reflexes, however, are only about 75 percent of the average human male.