Duncan is a dragon from Scotland. He runs a golf course. When Sir Loungelot dug a hole trying to his his golf ball, Duncan pulled the club from the stone of St. Andrews to chase after him. By doing so he proved that he was related to Sir William Furnace, as no one else could have pulled the club from the stone. He threw the golf club at Loungelot but hit MacBreath instead, who was about to kill Sir Burnevere. After this, Duncan became king.
- He is named after the king from the Shakespearean play Macbeth. Macbeth kills Duncan at the beginning to take his throne. In Blazing Dragons, however, Duncan's role is more similar to that of Malcolm, who becomes king after Macbeth is defeated.