A wizard had come to save them all. No one in Tristram knew much about him, only that he answered to the name "Mojo" or "Mr. Mojo." Ogden had a vague recollection of hearing the wizard mention that he belonged to the House of Risin.
Whoever he was, he seemed both confident and competent. He made several trips into the defiled cathedral, returning each time with a backpack full of treasure and reporting that yet another level had been cleared of the demonic infestation. The people of Tristram began to hope that, perhaps, this was a hero who wouldn't wind up gutted and hanging from Ogden's sign.
Then he ventured into the festering nest across the river. He returned four times, reporting strange alien monsters that even Cain could not identify. The fourth time he returned, he was seriously wounded and depleted of Mana. He described battling and being forced to flee from a monstrous creature that called itself the Defiler. The wizard had Pepin heal his wounds and Adria recharge his sorcerous might. This time, he promised, the Defiler would not surprise him and he would bring it down with the deadliest of spells. He did not return from the hive a fifth time.
Two weeks later, a swarm - or army - of insect-like monsters exploded from the nest and razed Tristram. The creatures called themselves the Zerg.