The Sin War is a trilogy of novel series set in Blizzard Entertainment's Diablo universe, written by Richard A. Knaak. It tells the story of Uldyssian as he is drawn into the battle between the Temple of the Triune, run by the Primus under Lucion; the Son of Mephisto and the Cathedral of Light run by the rebel angel Inarius. Uldyssian feels that both sides are corrupt and wants nothing to do with either of them. When he is accused of murdering one of their missionaries, he flees his home town of Seram as he begins to discover his own strange powers. He decides to teach others how to use it, and gathers many followers to him, but the Temple and the Cathedral want his powers for their own and will stop at nothing to get them.