Like her husband, she used to be a teacher. She taught at the New School of Cooking in Culver City.
Stephen married Karen in 1998. He added the character of Karen Plankton shortly after their wedding. Stephen called Karen "the funniest person he knows" and her sense of humor inspired the cartoon Karen's personality.
Mrs. Hillenburg is given "Special Thanks" in the credits of The SpongeBob SquarePants Movie. She is also mentioned as Karen Plankton's namesake in the audio commentary for "Plankton!" on The Complete 1st Season Disc 1 DVD.