Demons

Demons are like obedient dogs; they come when they are called.

— Remy de Gourmont

The spirit domain of Hades is populated by the demons. Demons are the Souls of the deceased that have fallen into the nine hells.
All Demons are Spirits of Evil, meaning they are all immortal and hard to change.

Description

Demons are the most numerous of all of Hades' denizens. They are created from the souls of evil mortals all over the brass realms, from those who have abandoned good and pursued their personal goals at the expense of others, from those who have sacrificed their futures for momentary pleasures. Demons vary wildly in their desires, powers and forms.
Demons have the ability to make deals with mortals, though they are always just in it for themselves and want to trick those mortals into giving up either their souls or something else that will raise the demon's status in hell.
Your soul, your fellow man's life and especially sacrificing the agents of Mount Celestia are always valuable offerings to a Demon and will get you whatever you might desire.

Demons are fundamentally evil. They are stuck in hell because they have committed heinous deeds in life and are unwilling to accept that they did anything wrong at all and would do it again if given the chance. When faced with eternal torment these beings want it to end, but more than that they wish to inflict the same upon others. They hate the innocent and the just for existing in peace while they must suffer. They are spiteful, petty, cruel and will take every chance to inflict pain on others that they can get.
It truly takes an Angel's patience to attempt to redeem a Demon.

Types of Demons

The Denizens of Hades are all Demons, though there are many subcategories.

Demon beasts

Demon beasts are the lowest form of all Demons. This does not mean they are weak, far from it. Instead, while they are dim-witted they are also strong, wild and animalistic. They are often created from the souls of Anzu that wandered into Hades or from the souls of minor evil creatures. They are often driven by one or more base desires, such as food, carnage, pleasure and the such and are only barely controlled by their masters.

Vermin demons

Vermin demons are cowardly beings that like to hide and attack from ambush using methods and terrain that their opponent is unfamiliar with. They have no honour and will try to wriggle out of any responsibility and promise and will lie, cheat and steal whenever they can.

Disease Demons

Disease demons are hideous beings that delight in weakening and tormenting others with sickness and poisons. They like using both poisonous knowledge as well as actual diseases to weaken others and watch them fall apart in the aftermath.

Trickster Demons

Trickster demons play games, they collect information, tempt humans into bargains with word-games and speak in riddles. They love playing politics, manipulating social dynamics, tempting mortals with forbidden desires only to then watch as they slaughter one-another.

Curruptor demons

Corruptor demons are the capturers, torturers and slavemasters of Hades. They capture lost souls, watch over the work of the enslaved prisoners given to them and torture those their Masters want punished - or just those they can get away with torturing. THeir favored tools are the whip and the prod, they use pain with great effect.

Soldier Demons

Soldier demons are the enforcers of the will of the Devils and Demon lords. They are organized, well-trained, experienced and cruel. They will follow the orders of their superiors without hesitation and complaint. They are armoured and armed with gear from the hell-forges. They are evil but they will keep their promises even without a contract.

Shadow demons

Shadow demons are masters of magic and forbidden lore. They veil themselves in darkness and delight in lording their knowledge and power over others, to tempt them into unfavourable bargains through curiosity and luring others into traps. They are very intelligent but are prone to hubris.

Devils

Devils are demonic nobility. They are the most 'civilized' population of hell. They are generally more intelligent and the most powerful demons are almost all devils.
Devils claim territories within Hades and rule over those little fiefs in their own ways. They exert tyrannical control over those in their territories and compete with each-other in dazzlingly complex schemes, that can span millennia. The Games demonic Nobles play with each-other, the twisting webs of alliances, betrayals and feuds simultaneously slow and pondering and lightning fast.

Devils also make contracts and deals with mortals, but they are a lot smarter about it than mere demons. Devils can afford to look into the distant future with their deals, for example.
Making a deal with a 'Hero', giving him magical powers completely for free can be more than worth it long-term. Spreading rumors about the benefits of a devil-deal can pay off massively in a decade or two, when some catastrophe (that may or may not be pure happenstance) drives the desperate to seek out alternative avenues to stay alive. Not to mention the not insignificant chance that anybody just handed immense power will fall to evil anyways without needing to sell their soul in the first place.
Asmodeus smiles upon the cunning.

Demon Lords:

Demon Lords are those extremely Powerful Demons that are granted the right to rule over one of the layers of Hades by Asmodeus. They are without exception supremely intelligent and powerful. Mess with them at your peril.

Behemoth is the Demon Lord of the First layer of Hades, Ubatil. He and his servants guard the gates of Hell and prevent intruders from descending further. He is invincible to all damage and stands undefeated in battle. Those given his favor gain martial prowess, skill and supernatural strength and endurance.

Dagon is the Lord of the second layer of Hades, Ivayok. He is the twister, the snatcher, the monster in the dark depths that is at all times waiting for its time. Those given his favor are often thieves, murderers and assassins. His gifts often physically transform the receivers.

Baphomet is the Demon Lord of the third layer of Hades, Munim. He is the lord of hunger and Prince of beasts, his body and mind honed to perfection and fully in tune with his savage nature. He is savagery tempered with intellect, brought to its full conclusion. His worshipers are granted youth, vigor, and opportunity to indulge in their most base desires.

Beelzebub is the Demon Lord of the fourth layer of Hades, Byathal. He is Asmodeus' spymaster and information gatherer. Nothing escapes his attention and his agents are all over the Brass Realms. The lord of vermin and disease deals in information and the means to gather it, cures for disease and the means to spread those selfsame diseases.

Lucifer is the Demon Lord of the fifth layer of Hades, Axal. A fallen angel overtaken with delusions of his own glory, he primarily seeks to tear down those that strive for the cause of good and virtue. Those given his favor are given beauty, cunning, political influence and an uncanny ability to deceive.

Abaddon is the Demon Lord of the sixth layer of Hades, Krunix. Titled 'The destroyer' his specialty is everything that brings ruin and death. Those given his favor command legions of demonic beasts or throw destructive magics to devastate their foes. He has a particular hatred for Angels.

Mephistopheles is the Demon Lord of the seventh layer of Hades, Ungromorn. Possibly the most knowledgeable scholar and most proficient magic user throughout all of the brass realms, Mephistopheles is a genius that knows no equal. He deals in secrets and forbidden magic with those that call to him for aid. It is said any secret imaginable can be obtained from Mephistopheles, so long as you are ready for the consequences.

Lilith is the Demon Lord of the eighth layer of Hades, Pandemonium. She is the Lady of Pleasure and Pain. She revels in excess and the suffering of her enemies. Those given her favor are given opportunity to indulge in the most vile pleasures imaginable in a downwards spiral of depravity.

Asmodeus is the Demon Lord of the ninth layer of Hades, Miril. Asmodeus is the greater deity of Tyranny and all things evil. He wishes for one thing above all else; to rule all there is, for nothing to escape his sight, for all to be at his every whim, for everything to be under his total control and utter domination.
Those that beg Asmodeus for his favor vary wildly in their reasons for doing so, and as a result how he deals with them.

Other Notable Demons

Mammon is often called the great demon of Greed. He is sometimes invoked by Merchants so as to strengthen their business, and very often all he demands in return is a portion of the profits.

A demon summoned from the hell-forges

An Avatar of the Demon Lord Beelzebub, Master of the Disease Demons

Appearance

Demons very wildly in their appearance. From the horrific to the surreal, from the bestial to the graceful. Their appearance is generally bound to their nature, however.

Devils are generally beyond such limitations. As spirits they have no true shape but they especially are able to shape-shift so as to fit more closely to the purpose of their current task. They thus mostly look human-like when interacting with humans.