Karen Plankton is one of the main characters in SpongeBob SquarePants, voiced by Jill Talley. She is the co-owner of the Chum Bucket, alongside her husband Sheldon Plankton. She is a sentient computer who is usually stationed in the Chum Bucket laboratory. She and Plankton are constantly scheming to steal Mr. Krabs' secret formula for Krabby Patties. Karen is typically the brains of the operation, coming up with complex plans to run Krabs out of business, although Plankton tends to take all the credit for them.
Karen is seen in two main forms: a big supercomputer on one wall of the Chum Bucket laboratory, and a portable computer with wheels. Her mobile form is currently the most common one. In both forms, she is mainly a blue-bordered black screen with a neon green line that moves whenever she talks.
Karen is Plankton's own creation, which he built from a calculator and a mass of wires. She was Plankton's first invention when he was in grade school, and they dated before he became evil. When Plankton decided to become a villain, Karen did as well because she wants whatever is best for her husband. Her system is built into most of Plankton's machines, including the Chum Bucket itself, so that she and Plankton can always be in touch. Specifically, Karen is a Mark II Surplus UNIVAC with 256 gigabytes of random-access memory.
Karen has many jobs at the Chum Bucket, including busser, chef and cashier. She also tends to stay more focused than Plankton on their mission of stealing Krabs' formula. Karen often reminds him to stay on task and encourages him to keep going when he loses confidence. Since she lacks a heart, Karen is usually unable to feel empathy for the people around her. She is a friend of Sandy Cheeks, who is also intelligent and interested in science. Karen has a habit of addressing SpongeBob as "the SpongeBob," although this has been phased out in the more recent episodes.
- In the first few episodes where Plankton and Karen appeared, Karen had noticeably less personality and more limited sentience.
- She was named after Stephen Hillenburg's wife, Karen.
- Her voice actress, Jill Talley, is married to SpongeBob's voice actor Tom Kenny.
- Karen's name is sometimes misspelled as an acronym ("K.A.R.E.N.") on merchandise. However it is just her name, and does not stand for anything.