|Karen's mobile form|
|Karen's wall form|
|Nickname:||Baby, Sweetie, Honey (all by Plankton)|
|Address:||The Chum Bucket, Bikini Bottom, Pacific Ocean|
|Gender:||None (female voice)|
|Color:||Blue and silver with black screen and green line|
|Eye color:||Green (when she has them)|
|Interests:||Lots of music, coming up with plans, playing cards, long walks on the beach with Plankton|
Karen is one of the main characters in the series. She is the computer system of Sheldon J. Plankton's laboratory, as well as his henchwoman, best friend and wife. She usually comes up with plans to steal the Krabby Patty secret formula, which Plankton tends to claim as his own ideas. She is voiced by Jill Talley, an actress who is also the wife of SpongeBob's voice actor Tom Kenny.
Karen was introduced in the episode Plankton! along with her husband. She is one of the two main antagonists. As revealed in the episode Friend or Foe?, Karen was just a security system when she started dating Sheldon. She has a Midwestern accent, in contrast to Sandy the Squirrel's Southern accent and Plankton's Eastern accent.
In the first movie, Karen informs Plankton of "Plan Z" by setting into motion the rest of the film's events. The movie also marks the first time Karen is seen in her mobile form; she is smaller and has wheels. Plankton also installed a button into Karen that would help him succeed in Plan Z and take over Bikini Bottom. In the sequel, she also plays a main role by powering the time machine that SpongeBob and Plankton use. She shares a heartfelt moment with Plankton when she is about to lose all of her power.
In the episode Welcome to Binary Bottom, Karen is a fish in an alternate reality where Bikini Bottom's inhabitants are all robots. Fish Karen is also voiced by Jill Talley.
She has a green wave on her screen to tell in which frequency she is speaking at. She has many buttons below the screen. Clem and the rest of Plankton's Cousins think that she is pretty. She has a built in analyzer, which can tell the ingredients in an item. In the majority of her appearances, Karen manifests as a large monitor in Plankton's lab or as her mobile, wheeled form. She is also installed into most of Plankton's inventions, such as Robot Krabs, Plankton's seashell submarine (as seen in It Came From Goo Lagoon), and the Chum Bucket's fist itself (as seen in 20,000 Patties Under the Sea). In the episode Goo Goo Gas, her baby face is shown as that of a calculator. As a baby, the only word she knows is "Hello". In "Welcome to Binary Bottom," she is a purple fish with a lab coat, black heels and hair and green glasses.
Karen and Plankton share a family. Karen has a mother-in-law named "EMILP", who is seen in "Single Cell Anniversary" as a computer program. Her father, Fredrick, has never been seen in the series, but appears in an issue of Nickelodeon Magazine. Karen's cousins-in-law are Plankton's Cousins and Clem.
- "Seaweed: 50% Sea, 50% Weed." (Later towards the end of the episode) "Plankton: 1% Evil, 99% Hot Gas." (Plankton!)
- "I heard this joke before!" (Fear of a Krabby Patty)
- "Just blink." (Komputer Overload)
- "Aw, I think you're just being overlydramatic." (Plankton's Army)
- "So, typical day of failure, I see, huh darling?" (The Algae's Always Greener)
- "Don't you dare!" (Single Cell Anniversary)
- "I never agreed." (The SpongeBob SquarePants Movie)
- "I suppose it would, if I had one."
- "SHELDON!! HA HA HA!"
- "The self-destruct coin slot has been activated. Ten seconds till detonation." (Imitation Krabs)
- "Here's your stir fry, little man!" (Karen 2.0)