Mordack is the main antagonist of the fifth game in the King's Quest series of computer games, King's Quest V: Absence Makes the Heart Go Yonder. He is a powerful wizard and is more powerful than his brother, Manannan.
Mordack's past is not revealed, but it is revealed that he used to play chess with Shadrack, who called him a "ninny at chess." He also was a good friend of Abdul Alhazred. Alhazred was vizier of the Land of the Green Isles and a brother of the Society of the Black Cloak. It was through his relationship with Alhazred that he met Cassima, princess of the Land of the Green Isles. He wanted to marry Cassima but she strongly refused. Enraged by this, Mordack kidnapped Cassima with help from Alhazred and made her work in his castle as a scullery girl.
When Mordack found out that his brother, Manannan, was turned into a cat by Prince Alexander, he sought to take revenge. To avenge his brother, Mordack captured King Graham's family- and the castle, and shrunk them and imprisoned them in a bottle in his laboratory on an island far from Daventry.
Graham finds out that Mordack wants to feed his family to Manannan(who is now a cat). He also finds out that he wants Alexander to try to return Manannan back to his original self. Graham tracked Mordack to his castle. He later fights Mordack in a magic duel. As a last resort, Mordack transformed into fire and surrounded Graham, but Graham summoned a rain cloud, which poured rain on Mordack and extinguished him. Killing him for good.
Mordack is considered as the most powerful villain in the King's Quest series. This is probably because it is stated that he is more powerful at magic than his brother, Manannan.