Dagan

Dagan, son of Belgin, Blood of Jangarak was the last High Old One or high priest of Dumanthoin in the lost dwarven kingdom of Thunderholme. He betrayed his people when a Shadow dragon 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, the dragon believing her to be an avatar of his deity. She then tore through the city slaying its inhabitants. No one knows what happened to Dagan, but it is assumed he serves her still, likely as one of her undead minions.