John Norman 
Chieftain [EPUB ebook] 

A peasant is sent to the arena, fodder for the carnage—but before the horrified gaze of noble ladies, the warrior named Dog slaughters headsmen, hunters, and beasts to win freedom as a full fledged gladiator. Then deep space rebels attack an Empire ship where Dog performs combat killings for the amusement of the passengers, and the gladiator becomes a rebel. Now a beautiful officer of the court finds her life depends on the mercy of Dog, the man she ordered put to death!