of featuring his anthropomorphic critters. In 1964, The Linus the Lionhearted Show began, featuring popular mascots from Post cerials, including Sugar Bear . In 1964, Underdog appeared, an anthropomorphic parody of Superman. In 1964 Hanna-Barbera introduced Peter Potamus . In 1965 Hanna-Barbera introduced Atom Ant , Secret Squirrel and The Hillbilly