The undead creature that would eventually be known as "Glashael" was once the human exharch to a mighty white dragon during the ending age of Xorvintaal. He served the dragon, hidden within Fjellraizad, and disguised as one of the dwarven priests there. Fjellraizad was a perfect stronghold, defended well from other dragons. Unfortunately, his patron was killed by a deadly poison. When the poison took the dragon's life, the warlock was cut off from his source of magic and was trapped in the dragon's lair.
In a desperate attempt to escape death, the warlock attempted lichdom and failed. He did not become a full lich, but he did manage to turn himself into a deathlock. Several hundred years passed and the temple went quiet. The dwarves had abandoned it. As time drew on, the warlock has sat in meditation, attempting to maintain his sanity. Unfortunately, he would forget much of his former life, including his name. He remembered only the name of his dragon, the mummified creature still coiled across her horde.
When he was discovered by a group of adventurers, he considered the release a blessing and swore to assist those who willingly released him. His powers are not as formidable as they were when his patron lived, but he still retained enough power to pose a threat to his enemies.
Despite his patron's death, the warlock, now calling himself Glashael, still harbors great, almost fanatical reverence for his dragon, and hatred for Cuelebre and her exharch Xungo who he still perceives to still be a rival.
As he travelled with the mortal party, he gained more and more power, eventually eclipsing his previous powers. The party began to perceive the undead warlock as a threat and chose to imprison him within the 6 Demon Bag.