Mephisto

Mephisto, the Lord of Hatred, is the eldest of the three Prime Evils, often assumed (though not confirmed) to be their leader. He seems the most intelligent, strategic and analytical out of the Three (although he is the weakest of them in-game). He is also the only known Prime Evil to have children, being the father of Lucion and Lilith.

Mephisto is also considered the most intensely evil of the brothers. So overwhelming is his evil that his malevolent influence can bring the dead back to life; these zombified beasts are filled with such anger for the living that not even a second death can quench their desire for pain and suffering.

Over the years, after having ensorcelled the Zakarum, he used his newfound power to bring the lands of Sanctuary under his heel through the martial power of warped Paladins, and sent the Zakarum deep into Westmarch, where his unwitting servant, King Leoric, would take over Tristram

An Evil Force when facing Mephisto.