Xannodos
Xannodos is located in a lair just up the steps beyond the Blood Twins.
Be sure to use the RIGHT-most blood hex to enter his lair (there will be two blood hexes next to each other) otherwise you'll end up somewhere you don't want to be!
His lair is permanently dark. He has adds that are either killed by Magic only (curse/magic missile only) or melee only.
Xannodos is known to drop an immortal helmet, immortal boots, a Poison Protection robe, and a mug.