Thea Stilton is a journalist and detective mouse in the Geronimo Stilton book and television series, as well as the protagonist of her own book series. She was voiced by Sarah Edmondson.
She is Geronimo's younger sister. She once went to Mouseford Academy, a highly prestigious school. She was a role model and a star student. She currently works for Geronimo Stilton's newspaper, the Rodent's Gazette, as a special correspondent.
At one point she came back to Mouseford Academy to teach a journalism class. There, she met five mouselings: Colette, Nicky, Pamela, Paulina, and Violet. They were all very different, so they became enemies with each other. Soon, a mouse named Hans Ratson disappeared, and the mice ran down the cellars to search for him. After a failed attempt, the five mouselings came again and scampered into a stone dragon's mouth, only to fall underground where they found Hans Ratson, who turned out to be the journalism teacher named Bartholomew Sparkle, who wanted to search the cellars for Viking treasures.
After the incident, the mouselings became best friends and named themselves the Thea Sisters. Thea left, but kept communicating and occasionally saw the Thea Sisters, who would go on adventures and solve cases and mysteries like Thea. To this day, Thea goes on adventures, usually dragging Geronimo into them.
Thea is obviously more outgoing and bossy than her brother Geronimo, who is usually cowardly. Unlike Geronimo, she loves to go on adventures and usually drags Geronimo into them. However, it is shown that she doesn't like her uncle Samuel S. Stingysnout's castle because he is so cheap he won't afford to heat up the place. Thea is also very caring to her family and her students, the Thea Sisters, and she is also very feisty.
Thea is a tall, slender and a gray furred rodent. She has a long snout. Her outfit often changes but in the books she is often seen wearing a royal blue jacket with a white fur collar, a lavender or pink scarf and blue pants.
In the TV series, her appearance is still the same as the book series; tall, slender, and grey-furred. Her clothing has varied from the book series, however. She wears a black jacket with white collars and a pair of yellow buttons on their tips, underneath it is a pink v-neck shirt with its collar folded slightly upwards to the outside, and a pair of dark grey pants on the bottom. She has a reddish-orange nose (color depends on lighting), a pair of purple irises in her eyes and has purple eyeshadow applied on the eyelids. When surfing, parasailing, windsurfing and scuba diving, she wears a wetsuit and a bikini when she is at the pool or the beach.
- She worn a Red bikini at the end of Barry the Mouse-tache.
- She also worn a Red and White bikini in Top Model Thea.
- She also worn a Purple wetsuit with Light Pink on the sides in Say, Cheese!, The Mermaid Mouse, The Disappearance of Nelson Napmouse, Dude, Where's My Shark? and Cheese Raker.
- She also worn a Purple and Black wetsuit in The Legend of Marzipan Island.