Plankton and Karen

Sheldon J. and Karen Plankton are a pair of fictional characters and the main antagonists of Nickelodeon's SpongeBob SquarePants franchise. They are voiced by Mr. Lawrence and Jill Talley, respectively. Their first appearance was in the episode "Plankton!", which premiered on July 31, 1999. They were created and designed by the marine biologist and animator Stephen Hillenburg, the creator of the series. Hillenburg named Karen after his wife, Karen Hillenburg (née Umland).

Plankton and Karen are the married owners of the unsuccessful Chum Bucket restaurant. Plankton is an intellectual planktonic Cyclops copepod and Karen is a waterproof supercomputer. Plankton shares a rivalry with Mr. Krabs, who owns the far more profitable Krusty Krab restaurant which sells a fictional burger called the Krabby Patty. Plankton and Karen often devise schemes to steal the secret Krabby Patty recipe from the Krusty Krab, but their efforts are always thwarted by Krabs and his employees.

Critics have praised the characters’ voices and dialogue together. They began as minor characters, but Lawrence developed their personalities throughout the show's early seasons and they eventually became the franchise's main antagonists. The Planktons play central roles in The SpongeBob SquarePants Movie, which promoted them both to main cast members in its credits, and in the 2015 film. Plankton and Karen are the lead characters in the Netflix feature film Plankton: The Movie, which was released on March 7, 2025.

[Plankton is a] complex, wounded character who is really looking for a friend in a way, but can't let that happen because of his evil front. He carries deep hurt underneath and doesn't want to let anybody know that.

Plankton is the nemesis and former best friend of Mr. Krabs. He is the owner of the Chum Bucket, a fast food restaurant located directly across the street from Krabs' restaurant, the Krusty Krab. The Chum Bucket primarily sells chum (bait consisting of fish parts), which is considered mostly inedible by the other characters. As a result, his restaurant is a commercial failure. Plankton's primary goal in the series is to steal the Krabby Patty Secret Formula so he can sell Krabby Patties at the Chum Bucket. His villainous efforts to do this are widely known within the show; fellow character Squidward Tentacles refers to Plankton as "the most hated thing in Bikini Bottom".

A running gag throughout the series is the fact that Plankton is smaller than the other regular characters. He is easily stepped on and sent flying back to the Chum Bucket with a mere flick of the finger. His small size has led him to develop a Napoleon complex, which is occasionally manifested as a desire for global domination. He is a skillful inventor and regularly builds machines, both to help him in his plots, and for his own personal gain. Although he uses his intellect for evil, Plankton did not start out as a villainous scientist; he built Karen, his first invention, when he was friends with Mr. Krabs in grade school, except in Plankton: The Movie, when he is hypnotized (which is also revealed that he was never able to be hypnotized), it was revealed that he made Karen out of a calculator, a roller boot and a potato, but gave her an upgrade in college, with a snarky chip, an evil chip, a smart chip and an empathy chip, the latter of which she removed earlier in the film. Prominent in his earliest appearances, Plankton's catchphrase is "I went to college!" He also has a pet amoeba named Spot who at first was a guard dog, but later became a retriever.

Plankton's roles are not exclusively antagonistic. Outside of business, at least sometimes and mostly in the more recent episodes, he seems to have a somewhat friendly relationship with SpongeBob, despite being technically archenemies but with SpongeBob trying in the meantime to help Plankton find his goodness or good side, usually failing for obvious reasons. In The SpongeBob Movie: Sponge Out of Water, Plankton allies himself with SpongeBob, initially to protect himself from an angry mob, but gradually warms up to SpongeBob throughout the movie. The movie has been described by The Guardian as a "buddy film" between Plankton and SpongeBob. Series creator Stephen Hillenburg considered Plankton over the years to be "more of a caricature of a villain" than a truly evil character.

When SpongeBob SquarePants premiered, Plankton was not part of the series' main cast. Plankton's voice actor, Mr. Lawrence, has stated that after producing Plankton's debut episode in the late 1990s, creator Stephen Hillenburg was unsure if he would continue to use the character. After recording it, Hillenburg was noncommittal, telling Lawrence: "We'll probably do another [Plankton episode] next year," Lawrence summarized Plankton's origins in 2015, saying that he "was only supposed to be in one or two episodes, but I was a writer on the show and I really liked this character". Following his first voice recording as Plankton, Lawrence drafted some of his own ideas for the character and passed them to Hillenburg. From then on, Plankton began to appear more often. Lawrence considers the third season the first in which Plankton is a main character.