She is a yellow slim plankton who has only been seen in live-action form.
According to Plankton, she is also evil.
When she was an adult she married Gordon Plankton, who would later have the nickname, "Papa Plankton."
Together, they had a child: Sheldon J. Plankton.
They may have had more children as Sheldon says, referring to his mother, "I was always her favorite."
According to Sheldon, she apparently taught her son how to be evil.
She was first mentioned in the game, Nicktoons Unite!, SpongeBob asks Sheldon what his mother would think of Plankton's actions and Sheldon says that he believes that his mother would be proud of him. He mentions that Sheldon was her favorite child. Later, he sarcastically says that his mother would be disappointed in him for being a villain.
She is mentioned again in Creature from the Krusty Krab.
She was then mentioned in "Plankton's Special Sinister Commentary." Sheldon mentions that when he was younger, his mother used to make chaos, destruction, and screaming.
She makes her first appearance in "Plankton. A Thank You Would Be Nice." She appears in a live-action clip shown behind Plankton.
She is considered to be as a real zooplankton in our world.
She appeared in the storyboard for "Plankton Gets the Boot", where she and her husband refuse to let their son in after Karen kicks him out. This scene wasn't featured in the actual episode.
She was completely unaware that Karen is her daughter-in-law.