Cletus Star is the great-uncle to Patrick, Gary the Snail, Ed Star, and Sam Star. He has so far only been mentioned by Patrick once in the episode "SpongeBob's Last Stand" and says he's hasn't been heard from for a very long time. He appeared to have been very wise, suggested by what Patrick claims he had said.
"Let not the heart wander lest the mind grow legs and follow." - Great Uncle Cletus Star