Calvin is a baby monster in the Sesame Street book My Baby Brother Is a Little Monster. Asleep when Big Bird comes over to get Calvin's big brother Henry, Calvin soon wakes up crying and begins to torment his brother.

He knocks over the blocks that he and Big Bird are playing with, yanks Henry's fur, smells bad when he dirties his diaper, and gets food all over everyone at lunchtime.

Delaying their trip to the park, Henry breaks down in tears and wishes that Calvin weren't around, but at the park the baby monster shows tenderness to his brother by uttering one of his first words, "En-wee."