|Voiced by||Candi Milo|
|“||It's a great day...for science!||”|
Dexter is the younger (but more intelligent) brother of Dee Dee. He is a boy genius and is fully devoted to science, but he is also very arrogant and takes great pride in his intelligence. In the series, he has a lab behind his bookshelf, where he performs experiments and creates inventions, which usually leads to trouble for him and his surroundings. His lab is usually devastated by his sister Dee Dee who just wants to play with his inventions.
Prior to FusionFall, Dexter has asserted himself as a world-famous genius and inventor, and is often considered to be the leader in the fight against Fuse. Before he hit his teenage years, Dexter founded his company, DexLabs, and became more and more withdrawn therefore after. Computress, Dexter's robotic assistant became his only companion.
At an unspecified time, the Hero has enlisted in a DexLabs time travel project. Before Dexter can program a destination into the machine, Dee Dee messes up the project (with her most famous line, "Ooooh! What does this button do?"), and sends the Hero into the far future where Planet Fusion's invasion has almost completely overtaken Earth. Dexter appears briefly and helps the Hero fight off his/her first Fusion, Fusion Buttercup. He is seen earlier helping Numbuh One, but disappears after Tech Square is devoured by the Fusion Invasion, signifying that he was lost after Tech Square fell. Shortly after on, a holographic message comes from Dexter for the characters to help the Hero back to the past.
Dexter can be found in Tech Square in front of Dexlabs, alongside Computress. He has constructed a home for his parents on top of his company building in order to protect them after Fusion Spawns started appearing around his old house in Genius Grove. However, his old lab there is still a Fusion target. His robots, the DexBots, are found all over the world.
- In the series he is short and is eight years old, but in FusionFall, he is around 13-15 and as tall as a teenager. Because of this, his Nano resembles his cartoon form more than he does (mostly in size).