Thea Stilton, Geronimo Stilton's sister, is a minor character in the Thea Stilton books. 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.