Fred is a greenish-brown fish (sometimes blue or bright purple) who was the first of the generic background character models to appear in the series. He is best known for screaming "My leg!" in certain situations.
His first appearance is the episode, "Reef Blower." However, he is barely seen in the episode, as he was in a car as SpongeBob zoomed past him. He's most often seen dining at the Krusty Krab. He was one of the first two background characters, and Harry was the other.
His name was revealed in the episode, "Patty Hype," where he was advertising the Shell Shack's talking and singing dog.
He is famous for the running gag in which he screams "My leg!" when something such as an explosion takes place which he first said in the episode, "Boating School."