Nosferatu is a character who only appears in the episode "Graveyard Shift." Nosferatu is a vampire from the 1922 horror film of the same name. In "The Graveyard Shift," Nosferatu is responsible for flickering the lights, which confused and scared SpongeBob and Squidward as the lights flickering was one of the signs of the Hash Slinging Slasher's arrival. He also appears in the one of the mini-games in the DS version of SpongeBob's Truth or Square video game.
In the 1922 film he originated from, his name was actually Count Orlok: "Nosferatu" is actually the Romanian word for "Vampire".