"Stone Cold" Steve Austin (voiced by himself) is a WWE wrestler and one of the main characters in Celebrity Deathmatch. He sort of acts as the show's scientist, making things like giant gundam-like robots, mutated super freaks, etc. He doesn't appear in the revival of the show, for once Nick mentioned he was too expensive.
Stone Cold appeared as a recurring guest commentator. One time, after having an argument with his boss Vince McMahon, he challenged him to a deathmatch and won. (see "Stone Cold" Steve Austin vs. Vince McMahon)