Dexter is an extremely intellegent boy who started to create fantastic inventions at the mere age of 1. He considers Albert Einstein to be his greatest influence. He is normally in conflict with his ditzy 11 year old sister Dee Dee. 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's favorite superhero is Major Glory.
In the end Michael offers Dexter to join because with his gizmos, gadgets and inventions the team can use them to stop villains and he accepts.