Night Queen

Many centuries ago, legend says a dark lady worshipped the dread god of greed and death, Faluzure, God of Death and Greed. The god promised to make the lady his queen if she brought death upon the world. Channeling the dark powers of her god, the lady raised an undead army that threatened everyone. A group of brave knights led by two knights, one of Pelor and the other of Kelemvor, united to fight back the coming darkness. The epic battle shook the lands before the knights finally managed to defeat the Night Queen. They couldn't kill her due to never finding her source of power. Instead they imprisoned her in a crypt near Mistyshire.
Centuries later, during The Great War, the Blood Soaked Massacre happened near the forgotten crypt. All the blood and violence woke up the slumbering Night Queen and gave her power to influence the world outside her prison. She manipulated those near Mistyshire and Rivershire to bring her people to drain their life force to gain enough power to break out of her crypt. Eventually her plans were foiled by Heroes. She raised an army of undead to raze Rivershire but were again stopped. Then the heroes killed her one last time and stole her source of the power, the Catalyst.