Fermat Hackenbacker is the main deuteragonist of the live-action Thunderbirds movie released in 2004. He is the son of Brains, and inherited his father's same fascination with technology. Due to his age, Fermat usually hangs around on Tracy Island, or attend school with his best friend, Alan. During the rescue near the end of the movie, Fermat piloted Thunderbird 2 by himself despite being extremely nervous. He proved to be a good pilot, even on his own and played a vital part in the Monorail rescue. He later aided Parker in defeating Mullion and was made an official member of International Rescue afterwards.
- Fermat was named after 17th Century French mathematician Pierre de Fermat.
- Fermat furthermore inherited his father's stutter, though to a lesser extent.
- While Fermat is shown to stutter when he's nervous, he seems to stutter less when he's more confident such as when he proved himself to be a capable pilot for Thunderbird 2 and easily accepted Alan's compliments.
- Fermat's mother and Brain's wife is not seen or mentioned in the film.