An advisor of Belial(The Lord of Lies) who exiled the three prime evils with Azmodan (The Lord of Sins), Duriel(The Lord of Pains) and Andariel(The Maiden of Anguish), has murdered and then disguised Deckard Cain since app.1200, alternatively, before Diablo has been secretly released from imprisonment by Archbishop Lazarus.
This advisor behind the scene, who is the brother/shade of Belial, is also known as "The Lord of Fakes" in Diablo III. Actually, he is only a greatly powerful fiend, hardly a lord. However, he crowns himself with "The Lord" due to his lineage. His aim is to balance The Sin War for the Burning Hells(to weaken both the three prime evils and angels), and to take the advantages for The Great Conflict.