Paksu was a minor character in The Father Christmas Letters. He was a polar bear cub who lived at the North Pole. He and his brother Valkotukka were nephews of the North Polar Bear. "Paksu" means "chubby" in Finnish.
Paksu and Valkotukka came to Father Christmas' house for a visit. They ended up never leaving.
Paksu, along with his brother, was mischievous. Father Christmas wrote of them that "they seem to be growing up just like their uncle."