Zhengyi

Zhengyi the Witch-King was once a Red Wizard of Thay, but later became an enormously powerful lich and servant of the demon prince Orcus. In the far north of Vaasa in northeast Faerûn, Zhengyi created Castle Perilous in just one night in 1347 DR, and summoned the various goblins, giants and orcs of the lands to him.

History
After raising an army, the Witch-King attacked the kingdom of Damara in 1348 DR, killing King Virdin and ruining the land. He was finally destroyed by a party of adventurers led by the Gareth Dragonsbane. Baron Gareth would eventually become King Gareth of Damara.

After effects
The Witch-King had hoarded many magical items during its existence, and after its destruction many items were discovered by determined looters. The items were often cursed and quite powerful, plaguing the lands of Vaasa and Damara for years afterwards. The lure of these magic items would become the back-story of the last two books of The Sellswords trilogy by R.A. Salvatore.