Grandpa SquarePants is the father of Harold, Sherm and Blue, and also the father-in-law of Margaret SquarePants. He is also the paternal grandfather of SpongeBob, Stanley, BlackJack, Todd, and Larry. He is only ever depicted in a cloud bubble, and depicted by SpongeBob in the episode "Rock Bottom." Grandpa SquarePants is suggested to be very wise. He is voiced by Tom Kenny.
He looks like a cleaning sponge, and has gray bushy eyebrows. He has green pants, red-orange socks with blue slippers, and glasses.
Grandpa SquarePants is first mentioned in "Rock Bottom," and is depicted in SpongeBob's mind in "The Sponge Who Could Fly." He is known for his wise sayings, which include "If we were meant to fly, we had have propellers on our heads or jet engines on our backs." in "The Sponge Who Could Fly", and "Never run for a bus, especially one that's going up at a 90 degree angle." in the episode "Rock Bottom."