The Tower of Althalaxx - Part 9?:

Kill Athrikus Narassin and bring his head to Balthule Shadowstrike near the Tower of Althalaxx.

I see. Well, if what you say is true, then now is the time to strike. I believe Athrikus resides at the top of the tower. Be careful though, he is surrounded by many powerful warlocks, much more deadly than the ones you faced before.

Balthule Shadowstrike: Athrikus Narassin is an ancient and powerful warlock. Perhaps we should wait for Delgren's assistance, but he obviously had much faith in you to send you alone.

Balthule Shadowstrike: With the death of Athrikus, I hope that the demonic forces in this area will be driven back. I have no doubt that they will regroup and return, but then we shall be even more prepared to meet their threat.