Mike Wazowski is a proud and confident monster, partly defined by his friendship with James P. Sullivan, whom he works with as his Scaring Assistant, and drives him through an exercise regimen like a strict coach.
They're best friends, room-mates, incredibly devoted to each other, although Mike seeks to improve their careers, partly because of the hard work and everything they've ever put into their jobs. He tried really hard to make sure they won the Olympic games so that he could prove he was able to be there. He is very confident and brave.
Mike has a romantic side, shown by his dating Celia Mae, whom he tells Sulley "is the one," presumably the one Mike wants to tie the knot with, and refers to as his "schmoopsie-poo," although he has a self-centered side, as he once commented "[he] oughta marry [himself]."
Like all monsters, Mike believes that human children are toxic with a poisonous touch, and his perfect world comes crashing down on his date with Celia when Sulley shows up with a human girl, whom he is much more afraid of than Sulley, believing the kid is "a killing machine," seeing her as a threat, to his and Sulley's lives, well-beings, their careers, referring to her as "it," a "thing," and not as a child, and was determined, if not desperate, to get rid of her, evident by wanting to put her back in the human world through any door, not just her own. Another reason he was warded from her might have been a pent-up resentment towards children when he realized they weren't scared of him.
His patience with Sulley was strained and tested to the point where Mike finally turned his back on Sulley but caved in, realizing that Boo was innocent, the bond Sulley had made with her was strong, and he followed Sulley back to help him save Boo from Randall Boggs and Mr. Waternoose .
After stranding Randall in the human world, and exposing Waternoose's plan to the CDA, Mike gave Boo his own fond farewell, tell her it had been fun, showing he too had come to care about her when they shared a hug.
Sulley is a top scarer under his boss Henry J. Waternoose, III, who is the CEO of Monsters, Inc. Sulley's best friend and sidekick is Mike Wazowski. His mother is Mrs. Sullivan (who is not seen in the movie, but mentioned by Mike) and his dad is the famous scarer Bill Sullivan. When he is first seen, Sulley is the top scarer at Monsters, Inc., responsible for generating the majority of scares that provide power for the city of Monstropolis.
In Monsters University, Randall is seen as a young and pimple-faced teenager. He sometimes wears his purple glasses, but stops wearing them near the end of the film.
In Monsters, Inc., Randall has 3 fronds, green eyes, 4 arms and legs and has the ability to completely blend in with his surroundings, making him invisible (as well as being able to cling to walls). He can also camouflage like a chameleon.
Henry J. Waternoose (or Mr. Waternoose and simply Waternoose) is the hidden true main antagonist of Disney/Pixar's 2001 animated film, Monsters, Inc. He is the CEO of the company Monsters, Inc..
Boo is a toddler who is curious and naive. She can speak, but has baby, gibberish vocabulary. The only actual words she says in the film are "Boo!", "Kitty!" and "Mike Wazowski!"
Celia is the receptionist at Monsters, Inc., which means she takes calls by monsters and may click buttons for monster voicemail. Celia often calls Mike "Googley Bear" and "Googley Woogley" calls Sulley "Sulley-Wulley", Mike often calls her "Schmoopsie-poo" and Sulley, in return, calls her "Celia-Weelia".
Roz is grumpy, especially to Mike Wazowski due that she is always bugging about paperwork.
George Sanderson is a character from Monsters, Inc. and its prequel Monsters University. He is a monster that runs afoul of the CDA's "Code 2319" (contact with a human child) several times, forcing the CDA to shave and scrub him to remove any trace of human contact.