He first 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 makes two cameos. He first appears kayaking, when the French Narrator's submarine knocks him over, to which he replies "Tartar sauce!" He then is seen on the beach at the end of the episode, and the tour bus runs over his feet. Patchy and Potty then show up, and Hasselhoff accuses Patchy of running over his feet, pulling Patchy's hat down, at the end of the episode he can been seen wishing SpongeBob a happy brithday.
He is also very famous outside of 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.
Role in video games
The SpongeBob SquarePants Movie video game
His role in the video game is identical to his role in the film. The only level he appears in is "Dennis Strikes Back!" After SpongeBob and Patrick get King Neptune's crown and a lift from David Hasselhoff, the Cyclops’ boot returns, along with Dennis! This time, he will throw several daggers at SpongeBob. Directly approaching him doesn't work, as he'll just leap to a different spot. The strategy to beating him is to use the bowling attack or deflecting his daggers using an upgraded spin attack. As Dennis' health decrease, he calls in Slammers into the arena. Once he is defeated, Dennis gets hit by an oncoming boat.
The only levels that he was in was both "Hold the Hasselhoff" and "The Return of Dennis."
Even though, David Hasselhoff appears both in the movie as well as the console version of the game, he is not directly mentioned in the PC game. His character is rather referred to as "......" even though he only appears on one artwork. This artwork at the end of chapter 7, "Shell City," shows a sillouhette of a cartoon version of Hasselhoff.
SpongeBob's Truth or Square
SpongeBob almost mentions him before getting interrupted by Squidward.
Role in books
He had the some role just like in the movie while in Are We There Yet? he was mentioned by SpongeBob.