Deathlords were once part of the paladin order. When Arthas took up the sword against his own people in Stratholme, the deathlords committed the same heinous act in many other cities across Lordaeron. The act of evil must have been so great that the evil transformed them into revenants, and they scattered to different parts in the world, haunting the regions they once walked on with human legs. Eldritch Deathlord turned from the Light when he slaughtered his own family, believing they were impure, therefore making himself an evil and banished outlaw.
Two artifacts were related to them in Warcraft III: The Frozen Throne, the Crown of the Deathlord and the Shield of the Deathlord. They both can be found in the Warcraft 3 bonus campaign respectively from an unnamed deathlord in the Echo Isles and from Eldritch Deathlord in Dustwallow Marsh, he can be found by crossing the lake with a secret shallows path that leads across the lake to a small island, he is guarded by two Lightning revenants guarding him. There is also another deathlords found in the bonus campaign, he is found in the Magistrate's temple standing before a throne.