Waylander (The Drenai Saga #3) by David Gemmell

All of Waylander's instincts had screamed at him to spurn the contract from Kaem the cruel, the killer of nations. But he had ignored them. He had made his kill. And even as he went to collect his gold, he knew that he had been betrayed.

Now the Dark Brotherhood and the hounds of chaos were hunting him, even as Kaem's armies waged war on the Drenai lands, intent on killing every man, woman, and child. The Drenai soldiers were doomed to ultimate defeat, and chaos would soon reign.

Then a strange old man told Waylander that the only way to turn the tide of battle would be for Waylander himself to retrieve the legendary Armor of Bronze from its hiding place deep within a shadow-haunted land. He would be hunted. He was certain to fail. But he must try, the old man commanded--commanded in the name of his son, the king, who had been slain by an assassin...

Waylander was the most unlikely of heroes--for he was a traitor, the Slayer who had killed the king...