Malthael becomes the main villain of Diablo III: Reaper of Souls.
Malthael was originally the Archangel of Wisdom and a member of the Angiris Council. After abandoning the High Heavens, he returns as the Angel of Death and leads the Reapers, an army determined to remove demonic influence by exterminating humanity.
His plan is the central threat of Reaper of Souls, Diablo III's major expansion. The story takes the player to Westmarch, where Malthael's forces attack the city and harvest human souls. The expansion concludes with the confrontation in the Pandemonium Fortress.
Tyrael is often confused with Malthael because both are important angels in Diablo III. Tyrael, however, becomes an ally of humanity, while Malthael is the expansion's antagonist.