|Spouse(s)||Lexi Carter (Fiance)|
|Children||2 Unnamed Twin Boys|
|Appearances||"Insane in the P-Brane", "It's Not Easy Being Green"|
Duncan is an epidemiologist and father of Lexi Carter's twin boys. He works for the World Health Organization. He is unaware, when he returns to Lexi's life, that she is pregnant, and she keeps him in the dark for some time, in part due to the Eureka version of maternity clothes, which completely hide the baby bump.
- Duncan was once referred to as Lexi's Doctor Who, in reference to the British television program, along with the initials of the World Health Organization.