Dexter used a gender-swapping machine to change Dee Dee into a boy thinking that she would be less annoying as a boy. After he did, Doo Dee turned out to be much worse than Dee Dee. He always beat Dexter up and abused him. Mom and Dad always loved Doo Dee more than Dexter. In the end of the episode, Dexter lured Doo Dee back into the machine with a football and changed him back into Dee Dee again. After that, Dexter kept loving Dee Dee because she was tolerable than Doo Dee and that he was lucky and glad to have her which left her confused as to his unnatural behavior.
Doo Dee is a muscular boy with blond hair. When he firsts appears, he is naked except for a towel with blue stripes wrapped around his lower waist. His clothes consist of a blue varsity jacket with two Ds on both sides, referencing his name. He also wears a white muscle t-shirt with red shorts, white socks with two red stripes near the top, and black shoes.
- Despite technically being a gender-swapped Dee Dee, the way he came into being was quite odd. After Dee Dee was placed in the machine, she simply disappeared and Doo Dee mysteriously appeared in the house the next day while Mom and Dad acted as though Doo Dee was always a boy, making it seem as though the machine not only changed her gender but reality itself.
- In the episode Old Man Dexter, he was technically mentioned when Dexter was trying to say Dee Dee's name right but kept getting it wrong. Doo Dee was one of the names he said.
- His relationship with Dexter is similar to the relationship between Lalavava and Mandark.