Duncan could refer to:
- King Duncan, a character in Macbeth
- The actor who played King Duncan as part of the Karidian Company
- Lee Duncan, who played Lt. Evans in "Elaan of Troyius"
- Duncan K. Fraser, who appeared as Engineer Walsh on Star Trek: Enterprise
- Robert Duncan McNeill, the actor known for playing Tom Paris
- Duncan Regehr, the actor who played Ronin on TNG and Shakaar Edon on DS9