This is a list of characters from the Disney/Pixar media franchise Monsters, Inc., including the 2001 film Monsters, Inc., the 2013 film Monsters University, and the 2021 Disney+ series Monsters at Work.

James Patrick "Sulley" Sullivan (voiced by John Goodman in the film series, the Disney+ series, Lego The Incredibles, and Disney Dreamlight Valley, Brian Cummings in the Monsters, Inc. video game, Joel McCrary in Disney Infinity and Disney Infinity 3.0, and Christopher Swindle in Kingdom Hearts III and Disney Speedstorm) is a furry, cyan-and-purple-spotted monster with a humanoid bear face, short devilish horns, dark blue eyebrows, and a cat-like nose. He has muscular limbs, a reptilian tail, dorsal spikes, and feline fangs. He excels at scaring children but is genial and sweet-natured.

Monsters University depicts a younger Sulley as a gifted but arrogant student, whose father Bill had made a name for himself as a scarer. While attempting to capture a school pet, he meets Mike Wazowski. What begins as a rivalry between the two monsters becomes a friendship that endures after they are both expelled from the school.

In Monsters, Inc., he is named the best scarer at the company, and following the events of the film, he leads the company's restructuring of utilizing laughs instead of screams to harvest energy. By the end of the film, he and Wazowski are named the company's joint chief executive officers.

In Monsters at Work, he retains the title.

Mike Wazowski (voiced by Billy Crystal in the film series, shorts, and the Disney+ series, Carlos Alazraqui in the video games, merchandise, attractions, and commercials and Noah Johnston as his younger self) is a green cyclops-like monster with a round body, two small horns, and thin arms. He has four fingers on each hand and three toes on each foot. Wazowski is depicted as diligent and intelligent, but also competitive, wise-cracking and stubborn. The former two traits are further displayed in Monsters University, while the latter three are further displayed in Monsters, Inc..

During a childhood field trip to the energy company Monsters, Inc., Wazowski becomes inspired to become a professional scarer.

He gets accepted into the Monsters University scare program years later, where he meets both James P. "Sulley" Sullivan and Randall Boggs. Wazowski grows jealousy towards Sulley for his cocky personality and slacker attitude, but expresses a liking for Boggs, his roommate. After failing one of the classes in the scaring program, Wazowski works out a deal with the Dean to re-enroll in the program on the stipulation that he wins the Scare Games, a competitive series of scare-based challenges. To participate, he joins the unpopular fraternity Oozma Kappa, which is later joined by Sulley, who also failed the class. Sulley and Wazowski begin to form a friendship as they compete in the games. During the final event, Sulley cheats on Wazowski's behalf. Distraught, Wazowski breaks into a door-lab to enter the human world in an attempt to find out if human children find him scary, which they do not.