He only appears in The SpongeBob SquarePants Movie. SpongeBob and Patrick fight Dennis on his back and legs. His butt gets stabbed by Dennis; he does not feel any pain, but he does ask SpongeBob and Patrick to "take it easy back there." At the end of the movie, he gets burnt by King Neptune.
He is also very famous outside the SpongeBob SquarePants world, but he only makes one appearance in the SpongeBob series. He seems to be part cyborg or android, as he is able to propel himself forward without swimming, like a motorboat. His pectorals extend outward, allowing him to place SpongeBob, Patrick, and King Neptune's crown in between them so they can reach Bikini Bottom in time.