"Two decades ago, my mentor faced the forces of evil and emerged victorious. I cannot hope to surpass his achievements, but I will try to bring balance to the raging forces that threaten to tear the world asunder in these days. The spirits are restless near Caldeum, I must quiet them."— Mehtan in his log(src)
Mehtan was considered to be a promising student, and was the only student ever taken by Xul. Mehtan later acknowledged that he could not surpass his mentor's achievements, but intended to nonetheless bring Balance to Sanctuary.
The Restless SandsEdit
"Well met, Master Mehtan. What have you discovered here?"— The Nephalem and Mehtan(src)
"Powerful spirits haunt these ruins. I was not strong enough to defeat them, but I was able to trap them. I fear the coven that invades the region will try to use the spirits for their nefarious purposes. But if you dare, you can try to put them to rest. Activate the totems to release the spirits, and be prepared to fight."
By 1285, Mehtan held the rank of Master Necromancer. The same year, he was in the Stinging Winds near Caldeum. Powerful spirits haunted the ruins in the area, but he was not powerful enough to defeat them (though he was able to track them). He feared that the Coven would try to use the spirits to further their goals.
Mehtan explained the situation to the Nephalem, instructing them to find and confront the spirits. The nephalem succeeded, and aided Mehtan when the Coven attacked. Mehtan could thus begin the work of freeing the spirits, though he feared the Coven would find other sources of power to exploit. Regardless, he bid his ally farewell.
The Necromancer's ChoiceEdit
"Death's minions threaten to overwhelm the living, so they must be culled. This beacon will draw many of Death's soldiers here to their demise. I was about to activate it."— Mehtan(src)
The Nephalem later encountered Mehtan in Westmarch. He was there to fight Malthael's Reapers by summoning them with a beacon, which the Nephalem activated. After defeating the Reapers, they spoke one last time before Mehtan departed.
Mehtan can randomly be found in the second act of Diablo III at the Stinging Winds. He initiates "The Restless Sands" event. In it, he and his skeletons will fight alongside the player if foes are near enough. At the end of the quest, he will drop his log.
Mehtan also has a chance of appearing briefly in Act V at the Hall of Dark Arts in Westmarch Commons. He starts "The Necromancer's Choice" event. At the end of the event, he will uncurse a radiant chest, allowing the Nephalem access to its contents.
He is referenced in flavor text of the Canem Mortem Liber.