Grandma Plankton is Plankton's paternal grandmother and Plankton's father's mother. She is first mentioned in the episode "Krabs vs. Plankton." She was called Gram-Gram in that episode. She only physically appears in the episode "Gramma's Secret Recipe." She is voiced by Laraine Newman.
She looks similar to Plankton, except that she has glasses, dentures, lavender-colored puffy hair, and wears an orange dress that has green polka dots.