Duncan ran a dojo at Duncan's Cabin outside of South Figaro near Mt. Kolts where he trained students in the martial arts. His two star pupils were his son Vargas and Sabin Rene Figaro. Sabin and Vargas were rivals, and argued over who would take Duncan's place as the new master. Each insisted Duncan favored the other. Vargas, convinced Sabin was to be chosen, apparently killed his father.
When they pass through South Figaro, the Edgar, Locke and Terra's party learns of this from Duncan's wife (an old man outside Duncan's cabin will tell the party also). They venture to Mt. Kolts where Vargas gets his comeuppance from Sabin, when he uses a Blitz technique on him.
Duncan did not die and the party can meet him in the World of Ruin, where he trains at his dojo now northeast of Narshe. He teaches Sabin his ultimate Blitz: the Phantom Rush. He then tells Sabin to defeat Kefka with every blitz he taught him.
- The Duncan bug can be triggered if the player visits him in the World of Ruin before recruiting Sabin.
- Duncan Harcourt was created by Kaori Tanaka, who also worked on the PlayStation game Xenogears. In that game, there is a character named Sigurd Harcourt. His brother is Bartholomew Fatima, a descendant of a character named Roni Fatima. Roni has a brother named Rene. Together, they live in a high-tech desert kingdom and possess a fortress that can travel through the sand. Harcourt, Roni, Rene, their desert kingdom and their mobile sand fortress are all homages to Final Fantasy VI.
- In the Dawn of Souls and subsequent remakes of the original Final Fantasy, Duncan is one of the automatic names the player can choose for the Monk job.
- One of non-playable characters in Final Fantasy XIII-2 is named Duncan.