Kherriun

Kherriun is a necromancer aligned with Hephernaan and the cult of Belhifet, charged with overseeing a secret program to build up a secondary army of undead slaves in the ruins of Kanaglym during the events of Baldur's Gate: Siege of Dragonspear. To this end, she bound the ghost dragon Halatathlaer to service, although she failed to properly master her reluctant minion.
If Gorion's Ward chooses to investigate Kanaglym, she fills the role of an optional boss fight, aided by assorted minions which include:
* Dark Magician 
* Undead Sentry 
* Zombie depending on whether or not you let the sacrificial ceremony play-out in its entirety.