The Jellien Leader was an alien and jellyfish-like monster who was the main antagonist of the episode "Planet of the Jellyfish." It kidnapped , , , , and everyone else in Bikini Bottom, except and and possibly a few others. It was the leader of the alien jellyfish known as Jelliens and almost succeeded in turning everyone in Bikini Bottom into jelliens until Sandy and SpongeBob showed up. He is first seen in a cave in Jellyfish Fields watching SpongeBob and Patrick.