Thundarr is a barbarian from parts unknown. All that is known, is that he was captured and enslaved by an evil wizard named Sabian. He was forced to fight as a gladiator, but he freed himself and lead a slave revolt. Although not specified, it is believed that Sabian's step-daughter Ariel gave him the Sunsword, which allowed him to defeat the wizard and his mutant army (as seen in the opening credits). He now travels with Ookla the Mok, and the sorceress Princess Ariel.
Thundarr is hot-headed and prefers to let his weapon do the talking for him.
Thundarr is a strongly-built man, with fair-skin, and blond hair. He is dressed in a sleeveless fur suit with leather belt, fur boots, leather or bronze armbands, and fang-teeth on a leather cord.