Grandpa is Caillou and Rosie's grandfather, Grandma's husband, Daddy's father and Mommy’s father-in-law.
He often tells Caillou about his daddy when he was little like Caillou. He apperars in several episodes including: Caillou's hiding place where he shows Caillou a fort hidden in a tree in the backyard Caillou loves hiding in it. In the episode Grandpa's Birthday, Caillou along with Grandma and Rosie, planned a surprise birthday party. Grandpa first appears in Caillou hates vegetables. In Season 4, he and Grandma would babysit Caillou and Rosie instead of Julie. He is usually seen wearing a blue sweater with a red collar, gray pants, and red shoes.
In the books about the characters sometimes seen at the end of the show, there is one about about Grandpa which Caillou mentions when he and Grandpa looked at the moon and that Grandpa gives the best hugs. Grandpa and Grandma live in a 2-story red house.