Mary Gibbs (born in Pasadena, California in October 5th, 1996) is an American actress and model who performed the voice of Boo in Monsters, Inc. She is also the daughter of Rob Gibbs, a Pixar story artist who worked on the said movie. As of 2015, Monsters, Inc. is her only film voiceover, although outtakes of her were used in Inside Out.
"Boo" is only a nickname of the character. In the film, she is seen signing her drawing "Mary" and in the novelization of Monsters, Inc., it is revealed that the character's real name is actually Mary Gibbs, the same as her voice actress.