The former Overlord of Hell, Lucifer, has disappeared and a new one must be found. Each player controls one mighty Devil Lord and the aim of the game is to have as much power as possible at the end, when the new Overlord is found.
Refer to the old background for more information, although some things on it has changed in the later versions of the game.
In Lords of Hell, each player controls one Devil, an immortal being of great power. All Devils have different powers and thus different strategies should be applied for each.
Asmodeus, the Arch-Fiend of Devilkin, is the oldest and mightiest Devil. For his status, all other Devils and inhabitants of Hell fear him and must obey him when he calls. He has also gathered the mightiest army of fiends and other inhabitants of Hell.
Mephistopheles, the Lord of the Whispered Promises is almost as old as Asmodeus, but while Asmodeus represent power and might, Mephistopheles is the master of smooth talk and negotiation, and most skillfully lures hapless Souls into his dominion and sometimes even hordes controlled by other Devils.
Baalzebub, the Lord of Flies and Deception, is the master of delusion, lies, and unclear answers and promises. He (it?) always finds a way to bend his words and rarely any promise wields what others originally thought. His home realm is easy to find as it is always filled with gigantic swarms of flies and other insects.
Mammon, the Lord of Greed and Vengeance, is an immense Devil patron of those who seek material wealth above all else. He has vast hordes of minions always expanding his dominion, and so great is the rage of Mammon if he is ever defeated in combat that most Devils usually leave him to be.
Belial, the Lord of Pain and Suffering, is the master torturer of Hell. So great is he power and art of torturing that even other major Devils fear him, as he is able to torture extra things out of them. Belial and his minions are also masters at torturing fresh Souls, turning them into twisted hordes full of rage and power.
Lilith, the Mother of Demons, is supposed to have been the first wife of Adam and later on wife of Asmodeus. She is well known for her beauty and skills at rituals and enchantments. Her magical powers are far beyond of other Devils, but she is also very seductive and can twist others to do her biddings.
Azazel, the Lord of Oppression, is yet missing from the game but is reserved for future expansions.
And last, but not least, Lucifer, the Rightful Ruler of Hell, might make his return at some point.