- "In a real Scare, you do not want to get caught by a kid's parent. And in this event, you do not want to get caught by...the librarian."
- —Brock Pearson warning his group about the Librarian
The Librarian (real name: Margaret Gesner) is a minor antagonist in Monsters University.
She is an elderly female monster who works at Monsters University's school library. The librarian resembles a tiny gray cephalopod monster with eight tentacles, gray hair, and wears a black dress and horn-rimmed glasses. Although she seems to be small and inoffensive when sitting at her desk, she turns out to be a lumbering giant about the same size as the library in which she works when she stands.
She hates noises inside the library. If she catches any monster being too loud, she will attack the offending party with her tentacles, and anyone who gets caught will be tossed out of the library and into a river facing the entrance. Whenever she gets angry, the Librarian will yell "Be quiet!" in a soft, whispery voice.
The librarian is involved in the "Avoid the Parent" challenge of the Scare Games, where the librarian's reaction to noise is exploited to emulate the danger of parents, and how a Scarer has to get along without being caught by one. Any team who is caught by her is thrown out of the library and disqualified from the competition.
When Oozma Kappa accidentally make a creak in one of the library's floorboards, grabbing the librarian's attention, they all start scattering and purposely make sounds from different parts of the library, therefore confusing and distracting the librarian while Squishy takes their flag unnoticed, and ultimately causing her to capture Slugma Slugma Kappa and toss them out of her library and into the river instead.
- The librarian bears some resemblance to Ursula, the villainess of the 1989 Disney animated film The Little Mermaid.
- Although the librarian's real name was not told of in the movie, in the Monsters University Fearbook, her name is said to be Margaret Gesner.
- The Librarian has similarities to the Pale Man from Pan's Labyrinth, because the hero has to sneak past her to get something. Her eyesight may be failing, but she knows when intruders enter her territory and captures them. Whereas the Pale Man devours children who step into his lair, the Librarian captures noisy students and throws them out of the library because it's her job.