Boo is a highly cute and innocent toddler who is curious and innocent. Although she can speak, her vocabulary is limited to baby talk. She says only a few words in the film like "Boo!", "Kitty!", "Ew" and "Mike Wazowski!". Despite her young age, she is quite advanced in some ways, such as being potty trained, as seen when she indicates to Sulley that she needs to use the bathroom without assistance.

Sullivan is a large, furry anthropomorphic monster with aqua fur and purple spots. He is a talented scarer from Monsters Inc, scaring children to generate energy. Sulley is about to break a record of scary energy generated. When dealing with some bureaucracy, Sulley finds a door unattended and enters - which causes the little girl who lives on the other side of the door (Boo) to enter the Monsters Inc factory.

He is a short lime-green spherical monster with one large green eye, two small horns on his head, and thin arms and legs attached to either side of his torso. He is Sulley's best friend, roommate, and assistant, helping him scare and succeed.

In Monsters University, Randall starts off as a timid, kind monster who is friends with Mike. However, after Mike befriends Sulley and stops spending time with Randall, he becomes hurt and turns on Mike, ultimately becoming his enemy. In Monsters, Inc, Randall is portrayed as greedy, ruthless, and cruel, as he is willing to harm children in order to capture their screams for energy.

Mr. Waternoose was the CEO of Monsters, Inc. He was the boss of Sulley, Mike and Randall, and Sulley's former friend, mentor and father figure. He was a character in Monsters, Inc., and was shown in a photograph welcoming Sulley and Mike to the company at the end of Monsters University

Baby Smitty is a small, light blue monster with four arms, black dotted eyes, and sharp teeth. He is a minor character in the movie Monsters, Inc.

Betty is a fish-like monster with an aquamarine body and purple spots. She has purple pupils in her eyes, two legs, two arms, and a blue fin on her back.

Life can be difficult for Blobby, who is a semi-transparent, pink, slimy jelly. Being careful when walking over grates is crucial as one slip can result in all the slime dripping through while the eyes, teeth, and hat are left behind at street level.

The CDA is a CIA-like organization whose primary duty is to locate and remove any type of children contaminant in the Monster World. They come in different forms and all wear bio-hazard suits to prevent contamination. If any human objects appear in the Monster World, they arrive to destroy it using a metal dome that causes whatever is placed under it to explode harmlessly and decontaminate any who come in contact with such objects. Their decontamination methods are often painful: anyone who has been decontaminated by the CDA will be forced to wear a plastic cone over their heads, similar to a pet who has undergone surgery and is not allowed to lick the wounds.

Chalooby is a factory cleaner who is diligent in cleaning up any slime trails in the corridors. However, he is known to leave a small amount of slime behind from time to time. He is a green, slug-like creature.

Chef is an employee at the exclusive sushi restaurant Harryhausen's. He has many tentacles, which allows him to prepare multiple dishes simultaneously. However, due to juggling cleavers and knives, one of his tentacles is frequently bandaged.

Chuck is a minor character in Monsters, Inc. He is a pink frog-like monster with four arms and works as an assistant to Claws Ward.

Dr. Frasenberger is an orange monster with a body shaped like a breadstick. He has no clothing, three stands of hair on top of his head, no eyes, ears that resemble fish fins, glasses, and a red bow tie.

Eric is a minor character in Monsters, Inc. He is a red, slug-like monster with five eyes and works as an assistant to Bud Luckey.

He is one of the monsters who works at the titular company and is known for his unique appearance, which includes one eye, four arms, and a lack of a mouth. He is the assistant of Bob Peterson's character, Roz.

Fungus, the name of Randall's deceased pet fungus, is a very cowardly, clumsy and incompetent character, who is bullied by everyone around him. He also makes a quick escape when he finds that Randall has been reprogrammed with the most dangerous people in space.

The monster really is a monster! This job really fits the bill for the trickster—he sweeps the streets tidy and then pops all the trash in his mouth as he goes, sometimes even swallowing the dustpan!

In Monsters, Inc., Harley P. Gerson is an employee at the company. He is yellow and orange skin, with two large feet, sharp teeth, a large mouth, and no arms.

It's possible that due to the presence of cameras, those being interviewed for a TV news segment are exaggerating their encounters with Boo. One person claims that Boo was able to destroy a car with lasers, while another monster suggests that Boo picked them up and violently shook them.

This monster, who claims to have witnessed the events at Harryhausen's, has multiple eyes, leading one to assume that they would have a clear view of what occurred. However, the individual states that their account of the events aligns with the accounts given by those previously interviewed on TV.

Jerry Slugworth is a supervisor of the Scare Floor F at Monsters, Inc. His job is to make sure everything is how it should be. He shows up each day to ensure all employees are working as they should, and fixes any problems that arise during his shift.

Ms. Flint resembles a Naga, with a red-orange color and a light orange underside that extends to her face. She has purple eye stalks with small bat-like flaps and is often dressed in a white v-neck shirt and black suit coat. She does not act in a snake-like manner and her lack of pants allows for greater mobility.

He is shown as the assistant of Joe Ranft and works on Scare Floor J.

He is ranked seventh on the Scarer's Leaderboard, and his assistant is Waxford.

Kevin is a character from Monsters Inc. who works at the company. He is the five-eyed slug monster, and the assistant of Theodore Pauley.

Little Mikey is a stuffed bear that belongs to Mike Wazowski. It is considered a bear in the Monster World.

He is a monster with a lot of tentacles and has a purple pom pom all over his face.

Celia is a former receptionist at Monsters, Inc. where she handled calls from monsters and managed voicemail. Mike often calls her "Googley Bear" and "Googley Woogley", Sulley calls her "Sulley-Wulley" and Mike often calls her "Schmoopsie-poo", in return, Sulley calls her "Celia-Weelia".

Marge is a Scare Assistant and a regular employee at Monsters, Inc. She has recently returned to work after serving on a jury. She is a friend of Mike's and one of the few female employees on the Scare Floor. Despite her bravery, she trembles when the CDA arrives at Monsters, Inc.

Needleman and Smitty are characters from Monsters, Inc. Both characters were portrayed by the late Daniel Gerson. Needleman has a thin build, light gold skin, a short tail, a large red nose, and two upward-pointing horns on either side of his head. Smitty has light green skin, four arms and resembles a slug. He has an orange fin-like hair styled over one of his eyes, in a hairstyle known as an "emo" when wearing his hat.

Mrs. Nesbitt is considered to be one of the least intimidating monsters at Monsters, Inc. She manages the school for young monsters with a combination of strictness and empathy. She has four arms which allows her, as a plump and purple-spotted monster, to comfort multiple children at once.

As a news anchor, he is known for his clear, confident delivery and his impressive eyebrows, which are possibly the largest in Monstropolis.

Pauley is a large purple monster that moves in a gorilla-like fashion. He has orange stripes and multiple spikes on his back, and has 16 removable eyes, which he mostly uses for scaring.

This blue dinosaur-like monster has removable teeth.

This couple are having their photograph casually taken at Harryhausen's restaurant when Boo jumped on the photographer.

Ricky Plesuski is a character in Monsters, Inc. and an employee at the company. He has a large mouth, big teeth, eyes on stalks, eight legs and no arms. He uses his sharp teeth as a scaring technique. He graduated from Fear Tech and previously worked at Fear Co.

Charlie is the assistant of George Sanderson, a green-skinned monster with two octopus-like arms, and four tentacles that serve as feet. He has snail-like eyes that can peek through two holes in his workman's hat. He is amicable and has admiration for the work of Sulley and Mike, and considers George as an older brother.

The current group of trainee Scarers at Monsters, Inc. have much to learn, as they are more easily frightened than able to scare. It is difficult to determine what causes them to be more startled - children or criticism from their superiors.

He is a big red monster with three eyes, but no mouth.

Rivera is an elongated, agile monster who works as a scarer at Monsters, Inc. He is the second tallest scarer on Scare Floor F, alongside Joe Ranft and George Sanderson, and stands just behind Sulley. He is an orange, slender monster with two eyes on small stalks, six long tentacles that act as arms, and four shorter tentacles that act as legs. His limbs have red tips and green stripes around his legs. He also has a turquoise snake-like tongue.

She is a large, yellow, slug-like monster with a tuft of white and gray pointed hair on her head. She wears a maroon sweater, black horn-rimmed glasses with supporting chains, and speaks in a rough, masculine voice.

George Sanderson is a character in Monsters, Inc. and its prequel Monsters University. He is a monster who repeatedly violates the CDA's "Code 2319" (contact with a human child), resulting in him being shaved and scrubbed to remove any trace of human contact.

Lanky is a scarer at Monsters, Inc. and is ranked tenth on the Scarer's Leaderboard. He is first introduced when the scarers are walking out to their stations. He is later seen being interviewed by a news reporter about the incident at Harryhausen's, where he exaggerates the story by claiming that Boo flew over him and used "its laser vision" to blast a car. He is a good friend of Claws Ward.

This monster's cold symptoms are quite unique - whenever he sneezes, fire shoots out of his mouth and nose. This means that anything near him, like a newspaper, can get burnt to ashes, and tissues are not an option. However, having him around can be useful as he can light the stove if you can't find any matches.

Monstropolis' monster kids love to play games in the street. A young monster's tongue is what they are using when there's no skipping rope available. Good thing, there's someone keeping them safe from the nearby apartment block.

He is a turquoise monster with crab-like legs with one eye, and the assistant of Harley Gerson.

Ted is a friendly monster that stands on his hind legs and likes to greet people. He is tall; very tall! He is taller than the buildings and all of the monsters in Monstropolis, but he doesn't mind it! Ted has to be careful where he walks so he won't squash somebody.

a prankster and former trainee scarer at Monsters Inc.

He sells fresh fruit and vegetables, and happily greets customers with a smile. Having four tentacles certainly helps when serving more than one customer at a time!

Lousy Randall gets exiled to the bad part of town in this funny new trailer for Monsters University. The residents aren't scared of large reptiles—they live by an alligator-infested swamp—and he soon gets a good hiding courtesy of the trailer mom and a shovel. To add to his misery, there's no way back. Mike and Sulley have destroyed the door to Monstropolis.

Claws is a monster with razor-sharp claws. He is also very good friends with Lanky Schmidt, George Sanderson and the other monsters in Peaceful Farm.

Waxford is one of the most trustworthy monsters in the factory. He's always very hardworking, which is why he's so reliable as Spike's assistant—and, if all else fails, he's got five perfectly good eyeballs on stalks to help him out.

This is Mrs. Wazowski, Mike's mother. A middle-aged green Cyclops-like monster, she is the same shape and design of her son but with hair similar to Roz and a pair of one-eye horn-rimmed glasses.

The Abominable Snowman (a.k.a. Yeti or the Edible Snowman) is one of the monsters from Monsters, Inc. He works at the mailroom of Monsters, Inc., until he is banished to human world for stealing Mike Wazowski's birthday cake and standing on Mr. Waternoose's shoes during a job interview.

He is a green three-eyed monster, and the assistant of Ricky Plesuski.