Kevin C. Cucumber was the leader of the Jellyspotters, and the hidden main antagonist of the episode "I'm Your Biggest Fanatic". He was speaking at a jellyfishing convention, in which SpongeBob and Patrick attended. SpongeBob was a big fan of him, and would do anything Kevin told him to do. He is ill-tempered, cranky, serious, nutty, helpful, good-hearted, funny, solitary, smart, caring, helpful, quirky, loyal, intelligent but later power-hungry, cruel, arrogant, sadistic, selfish, treacherous, murderous, calculating, envious, cold and ruthless.
He is a light green sea cucumber stylized to look like an actual cucumber and has a crown that is pale yellow with an orange outline attached to his head. He wears blue glasses along with brown colored shorts and has pink lips.
One day, he invited SpongeBob to go jellyfishing with the Jelly Spotters. He tricked SpongeBob into thinking he could join their club if he passed certain tests, simply so that he could humiliate and belittle him. This seems to be a habit of his, as many of his biggest fans have ended up stranded in a crevasse at Jellyfish Fields because of him.
However, all of Kevin's plans ended up with him getting stung by jellyfish one too many times, causing his hatred for SpongeBob to grow. Finally he snapped and said SpongeBob was ready for the final test: use SpongeBob as live bait to catch a queen jellyfish.
It was revealed the Jelly Spotters were using a robot queen jellyfish. Kevin and his friends then taunted and made fun of SpongeBob so badly by calling him a "loser," but when a king jellyfish fell in love with the robotic queen and attacked them, Kevin proved to be a coward and admitted that he was only in the club for the fashion.
When SpongeBob managed to ward away the king, Kevin was ruined when the Jelly Spotters ripped off his crown-like cranium and put it on SpongeBob. Although SpongeBob left the club, it's unlikely Kevin retained leadership of the club, as he lost the loyalty of his teammates.