Demons
Demons are one of the two types of Fiends - creatures from another plane of existence that feed upon the souls of mortals.
Location
Demons all reside in The Abyss and each layer is ruled over by the most powerful demon in each location. The Abyss is one of the Outer Planes that is reached from the Material Plane via the metaphysical passage known as the River Styx.
Description
There is no set form that Demons can take. Whilst many do appear to be vaguely humanoid there are many others that are slug-like, fungus-like or just writhing, indistinguishable masses of limbs and mouths.
Traits
Demons are best described as "raw emotion made manifest". They represent the base, unthinking, instincts that reside in all life: Anger, Lust, Jealousy, Selfishness, Greed (and it's counterpart, Avarice) and all the various forms of Hate.
All Demons, to some extent, personify chaos but will only ever work together to fight Celestials or, more commonly, Devils both of whom are in competition for their 'food source'.
Languages
All Demons speak their native tongue, Abyssal. Abyssal is a simple language with little nuance. A dictionary of Abyssal words would probably amount to no more than 10,000 words and most of the entries would translate to either "eat it" or "kill it". However, such a dictionary doesn't exist as Abyssal has no alphabet and doesn't exist in a written form; it has no need to as time is immaterial in the Abyss and no Demon is interested in what came before them or what comes after.
Demons that have existed for a few millennia of Material Plane time usually pick up some Infernal from their hated 'cousins', Devils. This language does have a written form and Demons are capable of learning this, given sufficient exposure.
When it comes to mortal languages, all Fiends share the ability to understand and converse in any tongue spoken by those that they can see. This ability is powered by a limited form of telepathy which is also how Fiends know a mortal's intentions and desires.
Names and Truenames
All Demons have a name that they announce to anyone that will listen and it is that name by which their personal reputation as a Demon is attached. Demon names, on the whole, tend to start off as long winded collections of syllables and gradually get shorter over time. The Cult of Lolth records that her original name was over 7 pages long originally but over the millennia has been reduced to the name she uses today.
Hence it is entirely possible to tell how important/powerful a Demon is by the length of their announced name.
However, all Fiends, both Demons and Devils, have a 'Truename'. A Truename isn't given or claimed - it's a verbal representation of the essence of the Fiend and knowing a Truename can give another Fiend, or even a mortal, absolute power over the Fiend. If the Truename is uttered a Fiend can be permanently bound to an object or place on the Prime Material plane, permanently banished from any plane (except the one they originally spawned in) or even have the souls they have accumulated over their existence disassociated from it - reverting the Fiend to their initial state of being. A Fiend can't be killed by the use of their Truename but removing several thousand years of progression probably feels much the same.
Obviously no Demon wants their Truename to be known to anyone. Luckily most Demons themselves don't know their own Truename and can't be forced to reveal it. Some mages, however, believe that they have found a way to circumvent this.
Behaviour
Demons are not planners; they exist in the moment and are fickle - heading where their appetites take them, sowing chaos where possible. Occasionally, a more powerful Demon will tell them where to go and what to do and they will do so for precisely as long as they have to and no longer. Demons hate being summoned by mortals and will only tolerate it as long as they get a payment that matches their greed (usually a sacrifice or twenty) or it allows them to wreck havoc upon the Material Plane.
Luckily Fiends cannot be permanently killed when on the Material Plane as their 'essence' as such is permanently tied to the Abyss and they will reform there after some variable length of time has passed. Demons know this and know that once on the Material Plane they can be as reckless as they wish with very few consequences. A loose Demon is a truly terrifying thing.
Notable Demons
There are far too many notable Demons to list but the more powerful ones have 'Cults' on the Material Plane that serve to funnel souls to their masters (or mistresses). These 'top tier' Demons refer to themselves as Princes (or, occasionally, Princesses) and all are exceptional among Demons both for their power and ability to forward plan. Each rules a specific layer of the Abyss. Among these are:
- Demogorgon - Prince of Madness, Layer 88
- Fraz-Urb'Luu - Prince of Illusions, Layer 176
- Graz'zt - The Dark Prince, Layer 46
- Jubilex - The Faceless Prince, Layer 528
- Lolth - Princess of Spiders, Layer 65
- Orcus - Prince of Undeath, Layer 113
- Yeenoghu - Prince of Gnolls, Layer 422
- Zuggtmoy - Princess of Fungi, 222