Gerhard Fishtrap is an alter-ego of Squidward, who only appears in the episode "Sold!"
He is a turquoise octopus who wears brown overalls, a yellow shirt, a mustache that is made out of a broom, and a dark brown hat with a pink feather attached to it.
When Squidward hears SpongeBob knocking on his door, waiting for someone to answer, Squidward quickly puts on clothes and supplies from his closet. He answers the door for SpongeBob, who invites himself in, and waits for dinner while Squidward goes into Patrick's house, where he changes into someone else. Squidward never dressed up as him after that.