SpongeBob's grandson is a character who only appears in the episode "The Great Patty Caper," where he is shown seventy-five years into the future. While the episode does not reveal the relationship of the character, the relationship 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. He also wears a red tie that is similar to a "Kentucky bow tie" on his pants.
SpongeBob's grandson appears only 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 formula (see the episode for more information). However, he is not interested in this story and cares more for his video game.