Celia is the receptionist at Monsters, Inc., which means she takes calls from 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".
Celia is normally a sweetheart, especially to her boyfriend Mike. While she may have an explosive temper when angered, she can calm down almost immediately when she is told the truth by Mike.
The snakes that make up her hair do not speak, but express their emotions with sounds they make. When they're happy they make chirping noises. When they're mad, they rattle and hiss. They often reflect whatever emotion Celia is feeling: When she is happy or mad, they likely feel the same way. Regardless, they still appear to have minds of their as shown when they briefly express terror when Celia considers getting a haircut, and relief when Mike respectfully objects.
Celia is a slender light magenta monster with sentient purple hair that resembles 5 snakes. She wears a green slick, sleeveless dress with a scale print design and a blueish green puffy collar. She has a single aquamarine blue eye. Celia has one thing in common with her boyfriend: they both have one eye. Their eyes are also of similar colors.
In the first film, Celia is celebrating her birthday, so Mike invites her to a Japanese restaurant called Harryhausen's, she is later heard announcing Randall Boggs as the top scarer, before telling everyone to forget it when Sulley gets more screams in a sleepover. Later she goes to her birthday date with Mike, but due to Boo being in the restaurant, the place is decontaminated by the CDA. One device that is made to make a large dome that would get rid of fatal germs, but could harm people without CDA armor, which is why Celia comes back to work the next day with serious injuries. She and her snakes are very upset with Mike about how the date was ruined. Mike kisses her to try to make her feel better, but she angrily slaps him. She later confronts him again with a near-tackle. While Sulley is hurriedly dragging them, Celia demands that Mike immediately explain what is happening or they're done. Mike instantly caves and tells her all about Waternoose and Randall's secret plot involving Boo (it was truly Randall, and not Mike, who ruined their date when he tried taking Boo to the Monster world). Initially, Celia doesn't believe a word he says but is then startled by Boo revealing herself. After hearing Mike reassure his love for her and seeing Randall following them, Celia now believes him that it was Randall who let Boo in, now realizing it was him who ruined their date, not Mike. She helps them by subduing Randall with a crowd after she feign-announces him breaking the all-time scare record, buying Sulley and Mike some time so they can get to Boo's door. She is seen again at the end of the film, having fully recovered and reconciled with Mike and tells him that a box full of magazines has just arrived. Both she and Mike are surprised to see that Mike has made the cover of the magazine. She kisses him and her hair tickles his face.
The year before the film takes place, she and Mike are supposed to have won the 7-legged race at the year's company picnic.
Celia also appears in the company play "Put That Thing Back Where It Came From or So Help Me" that her boyfriend has written, directed, and produced.
While absent from the film, a picture of Celia is seen along with her phone number in Mike's locker towards the end of the film.
Celia makes a minor appearance in the ride. Her voice is heard over the intercom telling the guests when they can enter the laugh floor.
- Celia's name may be a play on the word "Cecaelia." It might also refer to Scylla, a monster in Greek mythology known for snatching up those who strayed too close to her with mouths attached to tentacle-like limbs (somewhat like Celia's snakes).
- An early model of Celia showed that she was originally going to have a twin head named Welia.
- Sulley actually called her Celia Welia near the beginning of the film.
- According to the book Monsters Inc.: The Essential Guide, the five snakes serving as Celia's "hair" are named Amelia, Bobelia, Ophelia, Cordelia, and Madge.
- Celia makes a cameo at the end of Monsters University in a photo. Her phone number can also be seen.
- It is implied that Mike may have met Celia sometime after getting a job at Monsters, Inc..
- Celia having snakes for hair may have been a nod to the Greek mythology legendary figure, Medusa. However, unlike Medusa who is bitter and can turn people into stone, Celia is kind and does not have any abilities.
- A subtle reference to Medusa's petrification abilities was utilized in the movie when Celia approached Mike just before Randall discovered Mike's unknowing involvement in intercepting Boo, as Mike freezed up in terror while Celia was storming towards him in fury over the ruined date and glaring directly at him.
- Celia's age, according to the handbook, is likely 24, making her at least three years younger than Mike.
- The read-along version never shows any of the scenes in which Mike makes up with Celia. This could fool the reader into thinking that Celia didn't appear again.