The Nine Hells

The Nine Hells consists of 9 different planes of existence, connected together, each is ruled by a different demon lord from lesser in importance to most by the 9th level. The 9th level of hell is ruled by the Demon King Asmodeus, the most powerful demon lord in existence, and one of the most feared creatures in any realm.
The layers of hell have many purposes, but a key one is to contain the souls that Saraneth; Goddess of Death send to them that she deemed to evil to allow into the afterlife of Charr; God of the Afterlife. Most are kept in the first layer of hell, however with worse deeds the soul will be sent deeper into the layers, the torment growing far worse the deeper they go. Those who are sent to the 9th layer are the worst and most evil creatures to ever walk Aloreon and the torture they face is beyond mortal comprehension. With enough redemption souls can eventually leave the transcend the 9 realms and be rejudged by Saraneth; Goddess of Death, however any soul that has entered the 9th realm can never leave.
All this has lead to extreme corruption, unsurprisingly to many, even by Saraneth; Goddess of Deaths own words "I often now question more every soul I send deep into the depths of that realm, more often and often the armies of that self claimed king grows and grows with souls I recognize, souls I sent to him to repent."
The Lords of hell steal away souls they see potential in and add them to there armies of fiends and monsters, to the fear of many there is belief that even some of those souls in the deepest levels of hell are conscripted to Asmodeus's personal army.