What is SpongeBob's enemy called?

SpongeBob's primary enemy is Plankton, a small, scheming green plankton who owns the Chum Bucket, a rival restaurant to the Krusty Krab. Plankton is constantly devising plans to steal the Krabby Patty secret formula, often involving elaborate schemes that ultimately fail. Despite their rivalry, Plankton has moments where he shows a softer side, particularly in his interactions with his computer wife, Karen.