SpongeBob's grandson is a character who appears in the episode "The Great Patty Caper," where he is shown 75 years into the future. While the episode does not reveal the relationship of the character, it is confirmed in the credits.
His figure resembles SpongeBob, but he has a slightly different outfit, including a red cap. He does not wear a belt and also wears a red tie that is similar to a "Kentucky bow tie" on his pants.
He was born to a son or daughter of SpongeBob and his or her spouse.
Role in episode
SpongeBob's grandson appears at the end of the episode, where he is being told the story of where SpongeBob and Patrick went on a quest to find the Krabby Pattyformula (see the episode for more information). However, he is not interested in this story and cares more about playing his video game.
Relationship with SpongeBob
Their relationship is grandfather and grandson. SpongeBob's grandson does not seem to be interested in what happened in SpongeBob's youth.