Gorilla is a character who appeared in "I Had An Accident". He showed up out of nowhere disguised as Patrick and stuffed the real Patrick and Sandy into a bag, and smacked them on the ground and stomped on them, which made SpongeBob finally go outside. He also hangs out with George the Zebra, and they most likely are friends. When SpongeBob asked what the gorilla was doing underwater in the first place, the gorilla panicked and fled on George before they could question him any further, leaving everybody confused.
The Gorilla also appeared on episode "Friend or Foe?" on the Patchy segment, as Patchy's replacement. He is apparently a better cook than Patchy.