King Jellyfish is a massive jellyfish that lives in Jellyfish Fields. He wears a crown and a cape and has a vicious sting, and is the supposed leader of the jellyfish. He appears to be enemies with Kevin, but becomes friends with SpongeBob after giving King Jellyfish a piece of cherry pie made from bubbles.
King Jellyfish makes his debut in the episode "I'm Your Biggest Fanatic," when after Kevin abuses SpongeBob for thinking he caught a Queen Jellyfish, he falls in love with the Queen Jellyfish robot controlled by Kevin and after it is destroyed, becomes angry and starts chasing them. SpongeBob calms him by blowing a giant bubble pie. His reasoning is "Everyone loves pie!"
King Jellyfish also appears in the video game Battle for Bikini Bottom, as a boss that lives on top of Spork Mountain. SpongeBob needs to defeat him so he can heal Squidward's wounds with his jelly.