The Witch King is the epitome of evil in the Twin Kingdoms. Nekash was once a great half-elf sorcerer who served in the court of the Phoenix King of Ulthantis. Tormented by the thought of mortality, for he was half-human; Nekash actively sought out ancient and dark powers that might prolong his life. He eventually became the first necromancer to ever wake the dead. His powers grew great and terrible. Ever jealous of his elven cousins, he coveted the Throne of Fire. He greatly desired to exalt himself above the Phoenix King. A great civil war errupted with a third of the elves following Nekash, he repayed their loyalty by twisting their very beings into the cruel race known today as the Drow or Dark Elves in the common tongue. The great war ended with the defeat of Nekash and his drow and undead armies but victory came at a great price. The war resulted in the collapse of the Ulthantan Empire and brought about the decline of the high elves in the west.
Retreating to the daemon plagued lands of the east. Nekash built a great dark tower in the land of Nod and named it Darakdur. He allowed his dark elves to live below ground in a great cavernous realm today known as the Black Vault and he created the Spider Queen to rule over them in his stead.
2000 years have passed and Nekash labors still to this day in his dark tower of Darakdur raising undead armies, ensnaring beastmen, orcs, barbarians, and the daemon plagued warriros to serve him in his attempts at conquest. His agents scour the world, stealing souls to bring back to their master. Nekash rarely leaves his dark tower for he has long since become a liche.
The Black Duke is the lieutenant of the Witch King and the enforcer of his will. For the Black Duke is exactly that, the Witch King's will made manifest.