The battle against Belial takes place in Act II of Diablo III.
Act II moves the player from the wilderness and ruined town of New Tristram into the desert region around Caldeum. The act’s story involves political deception, imperial power, and the search for the fallen angel Tyrael. Its climax reveals Belial, the Lord of Lies, as the force manipulating events in the region.
Belial is one of the Lesser Evils rather than one of the three Prime Evils. His title reflects deception and concealment, themes used throughout the act’s plot. The player eventually confronts him in the Imperial Palace after navigating Caldeum and the surrounding desert.
Belial is sometimes confused with Azmodan, another Lesser Evil. Azmodan is the principal demon of Act III and attacks Bastion’s Keep, while Belial’s campaign is centered on Caldeum and belongs to Act II.