Zao'Kapazao, Vilebat Keeper is a unique Morlu Caster that appears in the Blessed Chancel in Act IV of Diablo III. He serves as the "boss" for the Hellbreeder Nest event, summoning minions throughout the encounter, which ends with his death. He and the event were added in Patch 2.2.0.
In combat, he has the Desecrator, Mortar and Jailer traits. Up to 4 times, usually after losing at least 25% of his maximum Life, he becomes briefly invulnerable - visually, shielded by a green force field - and teleports to a different corners of the platform. When approached, he summons 3 Corrupt Hellbreeders around himself, then becomes vulnerable again. Killing Zao'Kapazao ends the event, although any living nests and their Vilebat spawn will remain.