Gorun Stonekeep

This advisor to King Dagna of Mithral Hall arrived 6 months ago from citadel Felbarr, but turned out to be a duergar in the employ of the Great Whisperer. When the group discovered him and his Duergar allies, he turned invisible and tried to flee but was knocked unconscious by Kathra.
After interrogation, Gorun revealed that he served an aboleth named Illuun (the great whisperer) willingly, and that several other Duergar had joined as a cult to the aberration 15 years ago. He had been sent to Mithral Hall six months ago to manipulate the mad king into causing more chaos in the region. Kathra ended his life by smashing his skull in with her hammer.