Duncan is a minor character seen briefly in Underworld.
Duncan is a young Vampire struggling to rise through the ranks of the Death Dealers. He is assigned to monitor the Elders' Chamber, where the three Vampire Elders go to hibernate as part of the Chain. Selene lies to Duncan one night before the Awakening Ceremony is to take place, telling him that the Death Dealer master, Kahn, wishes to speak with him. She assures Duncan that she will "hold down the fort" while he's gone. Instead, Selene enters the Elders' Chamber and awakens Viktor in the hopes that he will put a stop to the plans of the Lycans and Vampire regent Kraven.
Upon learning that Selene was able to deceive Duncan and awaken Viktor, Kraven has Duncan dismissed from his post, and vows to have him tortured once his other problems pass. This never happens, however, as Kraven is killed soon after.
It can be assumed that Duncan likely dies along with the rest of the Coven when Marcus Corvinus awakens from hibernation and goes on a killing spree, killing every Vampire within the mansion, before burning it down.