This named has a chance to spawn after you complete the third step in the heroic adventure "Excavating an Answer" (if the named doesn't spawn, a PH will).
Can't range this guy, he pull/summons you near him. Tried him w/ 2 Cleric mercs on reactive, 1 Tank merc, 1 Druid, 1 Shaman, 1 Berserker. Even spam healing tank w/ dru/sham while zerker burned, tank merc went bye bye at 54%. Seems a bit overpowered for group content imo. Sacked mercs and 3 friends joined for the kill.