Unique Colossal Golgor found in Ancient Tower Study above the Greyhollow Island in Act V of Diablo III. It's the only Colossal Golgor in Act V, and has slightly different appearance. He can be nominated a bounty.
In combat, he has a Vortex affix, as well as greatly empowered Life and damage. To his advantage, the area is very small, with little to no space for maneuvering.