Grand Dad Plankton is the paternal grandfather of Sheldon J. Plankton, the father-in-law of Mama Plankton, the husband of Lily Plankton, the paternal great-grandfather of Chip Plankton II, and also the grandfather-in-law of Karen Plankton. He appears in the episode "One Coarse Meal."
His body is deep green and he has a light yellow eye with a red pupil. He also has a gray beard and three dark green dots on the top left side of his head.
When he was an adult, he married Lily.
They had at least two children, both sons. They are Gordon and Silas Plankton.
He, along with the other Plankton family members, are eaten by a whale.
He was also the grandfather of Sheldon J. Plankton and his numerous cousins.
Role in episode
He appears in Plankton's nightmare, where Sheldon is eaten by Pearl Krabs and he gets to talk to his grandfather, who was also eaten.
- He was completely unaware that Karen is his granddaughter-in-law.