Dagan

Dagan, son of Belgin, blood of Jangarak was the last High Old One or high priest of Dumathoin in the lost dwarven kingdom of Thunderholme.

He betrayed his people when the shadow dragon Aurgloroasa manipulated him into dedicating his newly anointed temple in the name of Null, the dragon god of death and undeath, and not his or his city's patron, Dumathoin. The priest then summoned Aurgloroasa, believing her to be an avatar of his deity. She then tore through the city slaying its inhabitants. The fate of Dagan was unknown, but it was assumed that he continued to serve her, likely as one of her undead minions.