Richard A Knaak - [Diablo - the Sin War 01] Birthright

Since the beginning of time, the angelic forces of the High Heavens and the demonic hordes of the Burning Hells have been locked in an eternal conflict for the fate of all Creation. That struggle has now spilled over into Sanctuary -- the world of men. Determined to win mankind over to their respective causes, the forces of good and evil wage a secret war for mortal souls. This is the tale of the Sin War -- the conflict that would forever change the destiny of man.

Three thousand years before the darkening of Tristram, Uldyssian, son of Diomedes, was a simple farmer from the village of Seram. Content with his quiet, idyllic life, Uldyssian is shocked as dark events rapidly unfold around him. Mistakenly blamed for the grisly murders of two traveling missionaries,
Uldyssian is forced to flee his homeland and set out on a perilous quest to redeem his good name. To his horror, he has begun to manifest strange new powers -- powers no mortal man has ever dreamed of. Now, Uldyssian must grapple with the energies building within him -- lest they consume the last vestiges of his humanity.