Duncan Douglas is Dexter's brother. He loves lifting weights and frequently bullies Dexter. He is terrified of Freakazoid, who beats Duncan up whenever he encounters him. His parents do not believe him that the "blue man" exists and think he may be crazy. He is close to his parents, and is enthusiastic about the idea of still living at home as a forty-year-old man-child lifting weights in his room, so that he can really bulk up and save some money.
Despite his fear of Freakazoid, he is present (along with his parents) at Handman's wedding, over which Freakazoid officiates. He is unaware that his brother and Freakazoid are the same person; however, in the fourth-wall-breaking closing to the series finale, Freakazoid openly refers to Duncan as his "jerky brother" onstage in Duncan's presence.
He doesn't seem to care at all for his brother Dexter.
He is voiced by Googy Gress.
- Main Title (cameo)
- Handman (cameo at Handman's wedding)
- The Chip, Part I
- The Chip, Part II (only speaks in reused footage from Part I)
- Hot Rods from Heck!
- Next Time, Phone Ahead! (nonspeaking)
- House of Freakazoid (nonspeaking)
- Italian: Massimiliano Alto