Zariel: D&D Collector's Series Descent into Avernus Miniature
Zariel: D&D Collector's Series Descent into Avernus Miniature - Rules of Play says:
Once a mighty angel charged ith watching the tides of the Blood War, Zariel succumbed to the corrupting influence of the Nine Hells and fell from grace. Asmodeus admired Zariel's passion for war and offered her rulership of Avernus. She accepted his offer and was transformed by Asmodeus into an archdevil. Zariel tempts mortals with power on the material plane and strikes bargains with them so she can bind them to her in the afterlife. She uses their souls to creatre lemures, which she can then promote to higher forms of devils.