Born in 1001, Duncan was the grandson of Maol Chalvim II through his eldest daughter, Bethoc, and a cousin of Macbeth. By 1020, he had already become the heir apparent to the Scottish throne, possibly after partially incapacitating Maol Chalvim himself. However, Duncan feared that Findlaech intended to elevate Macbeth to the kingship instead. To forestall this possibility, Duncan enlisted Gillecomgain the Hunter to assassinate Findlaech and rewarded him with the High Stewardship of Moray for his service.

In 1032, following the birth of his eldest son, Canmore, Duncan sought to secure his succession even further by ordering Gillecomgain to murder Macbeth. When Gillecomgain refused, Duncan retaliated by revealing to Macbeth that Gillecomgain was the Hunter responsible for Findlaech’s death. This disclosure led Macbeth to slay Gillecomgain himself. Duncan subsequently assumed Gillecomgain’s former role as the Hunter. In 1033, Duncan also took part in the assassination of MacBodhe, possibly acting under orders from his grandfather, the reigning king.

By 1040, Duncan had finally ascended the throne as King of Scotland. While walking on the heath with Macbeth and their sons, Canmore and Luach, he first discovered Macbeth’s alliance with Angel after encountering her and her clan in their stone sleep. Shortly thereafter, Duncan came face to face with the Weird Sisters, who foretold that Macbeth would one day become King of Scotland. With his suspicions fully rekindled, Duncan resolved to eliminate Macbeth once and for all and also ordered the destruction of Angel’s clan to prevent any future alliance against him.

Duncan’s assault on both Clan Moray and the gargoyles ultimately forced Macbeth and Angel into an alliance of necessity. Together, they confronted Duncan on the battlefield and defeated him. During the final clash, Duncan met his end when he struck a magical sphere that Seline had given to Macbeth. The artifact reacted violently, engulfing Duncan in a devastating blast of fire that destroyed him completely.