Caillou is the titular protagonist of the books, television series and related media of the same name. He is a 4 year old boy with a big imagination and likes learning new things each day. While he is mean towards his younger sister Rosie, the two always manage to get along with each other in the end. His friends are Clementine, Leo, and Sarah, though they tend to act like jerks towards each other sometimes.
He is the son of Boris and Doris, and the grandson of Rosemary and Grandpa.