What is the name of the little girl in Monsters, Inc.? Boo. Boo is a three-year-old human child who wanders through a closet door into the monster world and becomes the unlikely center of the film’s story.
Sulley, Monsters, Inc.’s top scarer, discovers Boo after she follows him home from a scare floor. Monsters believe human children are dangerous and toxic, so Sulley and his assistant Mike initially panic. They soon learn that Boo is not poisonous, and Sulley becomes protective of her despite the factory’s strict fear of human contact.
Boo’s real name is never revealed in the film. “Boo” is the affectionate nickname Sulley gives her, and it becomes the name audiences use. She calls Sulley “Kitty” and Mike “Mike Wazowski,” treating the intimidating monsters like unusual playmates rather than threats.
The conflict deepens when Randall tries to use Boo in the Scream Extractor, a machine designed to intensify and collect children’s screams. Sulley rescues her, exposes the danger at the factory, and ultimately returns her home. Mary Gibbs provided Boo’s voice, including her spontaneous childlike reactions.