Horadrim

The Horadrim is an ancient brotherhood of Magi that was formed by the Archangel Tyrael to combat the Three Prime Evils Diablo, Mephisto and Baal when they were banished to the mortal realm. Known members include Tal Rasha, Jered Cain and Deckard Cain. Deckard Cain is the last of the Horadrim mages and is schooled in the most obscure lore and history of the arcane.

The Horadrim was formed from the three major mage clans in the East by the Archangel Tyrael who tasked the Magi with defeating the Three who were devastating the mortal realm. Tyrael gave the Horadrim three Soulstones which would be able to contain the demons once they had been defeated.

Mephisto, the Lord of Hatred, was defeated and captured in Kehjistan, imprisoned beneath the Temple of Light in Kurast where the Zakarum monks were tasked with protecting the Soulstone.

Diablo and Baal escaped further west to Aranoch where Baal hid inside the city of Lut Gholein for three days. He then headed North into the desert a few miles before the Horadrim attacked him again. During the fight, one of Baal's attacks shattered the sacred Soulstone that was supposed to imprison him. The great mage Tal Rasha managed to subdue the Lord of Destruction, but the shattered stone could not contain the demon, so Tal Rasha sought to bind Baal within himself. Nor Tiraj, an Acolyte of the Horadrim, as well as the rest of the survivors imprisoned their leader within a tomb beneath the desert sands where his soul would wrestle with the demon for all eternity.

Jered Cain and the remaining Horadrim tracked Diablo further west to Khanduras, following the wake of terror that the demon spread as he went. After an epic battle, Diablo was imprisoned within the remaining Soulstone, and this was placed at the bottom of a large labyrinth within a cathedral in the town of Tristram.

The threat was gone and as time passed the Horadrim's numbers dwindled until only one remained, Deckard Cain, who remained at Tristram until Diablo came into the body of the Wanderer.