Sheldon J. Plankton and Karen Plankton are a pair and couple 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, cyclopic copepod, and Karen is a 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
Role in SpongeBob SquarePants Sheldon J. 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". "Get moving, genius, don't let him get away." "Befriend the SpongeBob, then when the time is just right, take the Krabby Patty!"
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. According to Mr. Lawrence, Plankton's 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 undergoes hypnotherapy (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 film, which was 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.
Mr. Lawrence has described Plankton as 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."
Development 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.
During production on SpongeBobs early seasons, Lawrence was the only staff member writing premises and outlines involving Plankton. At the time, he felt he "had to prove Plankton could survive as more than a one-note character". Since then, multiple writers have written for Plankton without Lawrence's involvement, including the teams of writers responsible for Plankton's starring roles in the first two SpongeBob films. Lawrence continues to write Plankton episodes, having said in 2015, "I'm not just his voice. I get to create how the character is written and how he evolves over time."
Preliminary design sketches for Plankton depict him in a robotic suit, with Karen's system built into it; that suit has yet to appear in the series. The suit functioned as a way to increase Plankton's presence, as one of Hillenburg's original intentions was for the character to be too small to see without a magnifying glass. As the series progressed, the animators enlarged Plankton's size, feeling that being microscopic was "not conducive to him interacting with other characters".
Voice
Plankton's voice is provided by show writer and actor Doug Lawrence, normally credited as "Mr. Lawrence". The voice originated as an imitation of one of his deep-voiced high school friends. On television, Lawrence first used this voice for incidental characters on Rocko's Modern Life. Fellow voice actor Tom Kenny found it amusing, leading to Lawrence's decision to use it when auditioning for roles on SpongeBob. Lawrence initially tried out for the role of SpongeBob during the series' pre-production, but Stephen Hillenburg wanted a more innocent voice for the character and turned him down. Lawrence continued to work on the show, voicing minor characters, eventually leading to him being offered the role of Plankton in his debut episode, "Plankton!". He describes Plankton's voice as a "combination of Gregory Peck and Tony the Tiger."
When "Plankton!" was pitched to Nickelodeon, Hillenburg had already decided that he wanted Lawrence to play Plankton. However, network executives wanted a guest star to provide his voice since he was set to appear in only one episode. Lawrence mentioned in an interview with fellow SpongeBob actor Thomas F. Wilson that the studio said, in his words, we could stunt-cast this. You know, we could have Bruce Willis do this voice.' And Steve [Hillenburg] was just like, 'it's Doug, don't you hear it? This is the character!
Reception Critical response Bettijane Levine of The Los Angeles Times wrote positively of Plankton's portrayal, calling it poignant rather than genuinely immoral, describing him as a "town meanie... but mean is different than evil. There is no evil, not even a sense of menace, in SpongeBob's soggy, safe world." Boston.com writer Jamie Loftus had mixed feelings about Plankton in a 2015 article, asserting that while "almost every episode featuring tiny supervillain Plankton is highly formulaic", he never "gets old".
James Poniewozik of Time magazine commented on Plankton in a 2001 article. He noted that "no one thinks it's strange that the town villain, the megalomaniacal Plankton, is a one-celled organism" as part of the "colorful, goofy" atmosphere of the program. In an article for The A.V. Club, Zack Handlen stated that "the humor of Plankton comes from how his operative ambitions are constantly thwarted by a naïve, trusting kid". In 2015, Entertainment Weeklys Hillary Busis named Plankton one of the most devious characters on television, adding in her commentary that he is "voiced to wicked perfection by Doug Lawrence". José Antonio Gómez Marín of El Mundo favorably compared Plankton's plans to the stories of Georges Simenon in a 2013 article.
In his 2011 book SpongeBob SquarePants and Philosophy, political scientist Joseph J. Foy argues that "Plankton may actually be the unsung hero of the series, and SpongeBob the true villain." He compares the character to the Nietzschean Übermensch, taking note of his mental superiority compared to the other characters in the show, and questions how Plankton is only "judged as bad because, no matter how many great things he accomplishes, his intentions are deemed ignoble". Foy concludes his analysis by criticizing the fact that "SpongeBob is praised as noble for trying to hold Plankton back."
Karen
Role in SpongeBob SquarePants Plankton is married to a waterproof computer, Karen, who is also his sidekick and best friend. She is often referred to as Plankton's wife, but according to Plankton, WIFE is an acronym standing for "Wired Integrated Female Electroencephalograph." Karen is Plankton's own invention, assembled 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. Her system is built into most of Plankton's machines (including the Chum Bucket itself) so that she and Plankton can communicate while the latter is on a mission. She is a Mark II Surplus UNIVAC with 256 gigabytes of random-access memory.
Karen takes on various jobs at the Chum Bucket, including busser, chef and cashier; she rarely has to fulfill them because of the restaurant's unpopularity. She also tends to stay more focused than Plankton on the core 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. Her interactions are not limited to helping Plankton, however; she is a friend of Sandy Cheeks, who is also intelligent and interested in science.
Karen is more competent than Plankton in formulating plots to steal the Krabby Patty recipe. Most of his effective plans have come from Karen, including "Plan Z"—the only scheme to result in Plankton successfully stealing the formula and using it to his advantage—in The SpongeBob SquarePants Movie. Nonetheless, he tends to take credit for them, much to her dismay. Karen has effortlessly stolen Krabs' formula without Plankton's help on many occasions, but her husband always inadvertently gets in the way. Because of their contrasting behaviors, Plankton and Karen have a tendency to argue. Tom Kenny, SpongeBob's voice actor, has called their marriage "Honeymooners-like".