Zariel, Archduchess of Avernus

Zariel was the lord of Avernus, an archduchess dedicated to winning the unending Blood War between devils and demons. She was originally an angel of the Seven Heavens before transforming into an archdevil and falling to the Nine Hells.
Zariel was responsible for The Savage Seven's infernal contract that bound them to the nine hells upon death. After finding her sword and failing to redeem her, they destroyed her alongside Arkhan the Cruel.