Dexter is a boy genius that eventually became member of the house of geniuses, he and along with the genius invent weapon and gadget to help the Society fight off the Orgs,
Canon bio[]
Dexter, an eight-year-old genius boy, who has a secret laboratory (which he pronounces with a stress on the second syllable, luh-BOAR-uh-tor-ee) filled with highly advanced equipment hidden behind a bookshelf in his bedroom. Access to this never-ending laboratory is usually achieved by speaking various passwords or by activating hidden switches on his bookcase (such as pulling out a specific book). Dexter is normally in conflict with his ditzy older sister, Dee Dee, who always mysteriously gains access to his lab no matter what he does to try to keep her out. Dee Dee eludes all manner of security and, once inside, delights in playing in the lab, often destroying all of his creations. Despite her hyperactive personality, Dee Dee sometimes makes more logical decisions than Dexter, or even gives him helpful advice. Dexter, though highly intelligent, often fails at what he has set out to do when he becomes overexcited and makes careless choices. He manages to keep the lab a secret from his clueless, cheerful parents, who amusingly never notice any evidence of the laboratory, even when it was right before their eyes. Despite coming from a typical all-American family, Dexter speaks with an accent, a reference to Tartakovsky's own accent that he spoke with during childhood.
Dexter has an arch-nemesis, a boy from his school who dubs himself "Mandark", who lives down the block from Dexter and has a secret laboratory of his own. Mandark's schemes are generally evil and are designed to gain power for himself while downplaying or destroying Dexter's accomplishments. Dexter often makes better inventions than Mandark, but Mandark tries to make up for this by stealing Dexter's inventions. Mandark is also in love with Dee Dee, though she prefers to ignore him and never returns his affections. As the series progressed, Mandark's schemes became significantly more evil, his laboratory darker-looking, industrial and angular, in contrast to his original brightly-lit lab which had more rounded features.
Appearence in Ultima[]
Dexter once had bitter rivalry with other boy genius in the Society, Jimmy Neutron. for building the Geniuses's construction lab and design the Safe House, eventually they resolve their problem by working together after few glitch, even though, the rivalry stance somehow still appearing when they're arguing their project invention