From her first appearance, Thalia appeared to be very indifferent to many of the happenings at Monsters, Inc. She outright disliked being anywhere near her mother's place of work, but would put up with it to please her. She is a very good judge of character, however, and tells it like it is. While she is not completely devoid of humor, it does take some effort to get her to crack a smile. Later, she does open up and admires people who are honest with her and develops an appreciation for the company and the people in it.
Thalia, in some ways, resembles a tiny version of her mother. She is purple in color, with lighter purple lines going across her body and has the same unusual eyestalks with the small green bat-like flaps behind them. She lacks her mother's overbite and nostrils, instead bearing a flat face, though she still has tiny sharp teeth. She has arms with four fingered hands, but instead of having a snake body, she has a small planted bottom with four toe like appendages. Just like Ms. Flint, however, she apparently slides around.
- Thalia is voiced by Hadley Gannaway, the daughter of series developer Bobs Gannaway.
- After Hadley played young Anna in Frozen II, she's also played Thalia in this show.
- The only monster that Thalia seems friendly with is Otis. This is most likely because Otis is voiced by Bobs.