Cadhul the Deathcaller, Shepherd of Defilement, is a Unique Dark Summoner found in the Southern Highlands in Act I of Diablo III. He has a chance to appear at the same location, should the stone platform appear instead of Ancient Pyre.
In combat, he has Desecrator and Plagued affixes (which cannot normally be found on the same monster). In addition, his five followers shield him from harm, summoning Hellions until they are all killed.