Gillecomgain was once a young peasant boy tending his father's farm when he heard the animals in the barn making a racket. He rushed in to find out what was happening and discovered a lone gargoyle raiding the barn for food. She promptly slashed him across the face, permanently scarring him, and he vowed revenge against the gargoyle later known as Demona, and all of her race.
Gillecomgain made a name for himself as "the Hunter" by destroying gargoyles across Scotland. He came into the service of Prince Duncan as an assassin, and in 1020 was sent to kill Findlaech of Moray. As a reward, the prince awarded Gillecomgain high stewardship of Moray. Prince Duncan also arranged for Gillecomgain to marry Gruoch.
After the two were wed, the Prince asked Gillecomgain to murder Macbeth, but he refused and implied he would reveal Duncan's treachery. Duncan, enraged, sent Macbeth after Gillecomgain, revealing him as Findlaech's murderer. Macbeth sought out Gillcomegain at Castle Moray and the two battled. Demona, present at the urging of the Weird Sisters, discovered that Gillecomgain was the Hunter and threw him from the battlements. During their fight, his mask was removed exposing his facial scars, and he asked Demona if she remembered him because the scars were her "handiwork". Demona spitefully said she didn't remember. Gillecomgain, in a final vengeful attempt, tried to drag Demona to her death, but she was saved by Macbeth, and Gillecomgain fell to his death.