Written by The Mad Professor
No living creature (dragonkin, Dae'vol, or human) really knows how demons came about. As such, speculating about the 'creation' of demons is a popular distraction for bored mages and sorcerers. Those attempting to move from theory into fact run into a big problem: no one wants to talk. Gods ignore such questions as far beneath their dignity. Demons seem to treat such questions as invitations to spin wild yarns; often giving entirely different stories to the same person on different days, it possible they do not know or care. There are rumours of unthinkably powerful and ancient demons who've retreated into a sort of hibernation. A supremely powerful sorcerer (one able to challenge one or two minor demigods) might be able to compel them to reveal their history. Or just end up as lunch.
While there have been several attempts at categorising and understanding the underlying order of the Infernal Realm, it has generally been conceded that such lists tend to lose their relevance about two seconds after they're penned. The few constants that exist generally rely on what demonologists refer to as the Demon Lords, a few demons so powerful that they rarely lose their power in the constant hierarchal manoeuvrings, these Lords are among the most potent demons that exist and are rarely unseated from their various positions of power. It should be noted that "are rarely" does not necessarily mean, "are not", their power can wildly fluctuate. This lack of a coherent social order means that words such as imp, succubi, archdemon, and so on have little meaning. Something which was once one, may later be the other. Gender, appearance, such things are almost infinitely malleable for most demons. Most have certain forms that they have set as their own, however, and anyone else trying to use it may end up earning a new enemy, fast. The Infernal Realms exist in a constant state of warfare (on several levels, not just the physical), wherein the various inhabitants constantly scheme for power over each other. As long as a demon remains within the confines of the Infernal Realm they remain immortal and immutable, in order to gain knowledge, power or achieve growth they have no choice but to leave the confines of the Infernal Realms and venture out. Contrary to what many might think this constant state of warfare is not something they only wait to take out on other beings, a demon has very little to gain by randomly killing humans when having them join their ranks will serve them much better.
The Infernal Realms
The Infernal Realms are vast and unmappable. It resides in almost perpetual darkness and travellers are warned against entering it with a source of light, salt, or anything which produces music. It has acquired such sundry names as the Shrieking Darkness, the Howling, the Dark Plane and similar. The gloom is occasionally lifted by far off flashes of fire and lightning as demons employ such weapons against one another. What some describe as the ultimate horror of the Infernal Realms is realising that there is no ground on which to tread. Instead the constantly shifting ground consists of gigantic demons which have entered a hibernation for an unknown period of time, or just smaller demons fighting between themselves in slow motion. It's generally considered to be a bad idea to attempt any kind of psychic activity in the Infernal Plane as traps and psychic warfare is constantly happening. Though this is partially to blame for the many different, but illusory, descriptions of the Infernal Realms.
The creation of a demon is no simple thing. All demons begin their existence as something else, they become a demon through entering into a contract with a demon, whereby they sell their soul for services rendered. It is this contract, to which even the gods must bow, which allows the person who signed the contract to become a demon upon their death if the demon has fulfilled his side of the bargain (to the letter if not the spirit). Demons cannot force someone anyone to become a demon, they must sign the contract of their own free will. This does not stop demons from using everything from blackmail, lies, loopholes and all manner of temptations to get someone to sign the contract. The contract must be signed in blood and is vital to the demons. They will do quite a lot to get hold of a soul, though if too much is asked of them, they will generally find someone else who is easier to deal with. There is never a lack of people who are willing to sell their souls for a hand up. As demons they have much to offer those that take an interest, some can teach all manner of esoteric and mundane knowledge, others can offer power, others can bargain with the lives of enemies and loved ones. Once the terms of the contract have been filled however, there is little that any demon is willing to do for the person who signed, they've already got what they want so they see no reason to continue helping them. In lieu of a contract though, the demon will often be satisfied with taking a small piece of a person instead, memories, skills, things like these are gladly consumed and used to enhance their own power, often leaving demonologists as little more than hollow shells waiting to sign the contract their demonic consorts offer them. Once a new demon is created, the power from this is spread among the demons who helped to make them a demon, effectively making them stronger. The new demon will be relatively weak as compared to other demons and is generally referred to as an imp, though as long as it remains in the Infernal Realm it is immortal and cannot be destroyed. If a demon is returned to the Infernal Realm it will generally always recover from its injuries (though it may become weaker because of it). Their new form and abilities do tend to mirror what they did in their previous life, a wizard will become a demon capable of wielding supernatural powers, a soldier someone capable of dispensing great destruction, a courtesan may become a succubi and so on.
Speaking of any common thread in the appearance of demons is relatively counter productive. They wear bodies much as humans wear clothes, and are prone to changing them just as often. Most will have one or a few relatively permanent shapes that they prefer however. Demons are bound by certain rules when changing their appearance however, they can never look like what they originally started out as. Someone who was originally a human will never be capable of looking entirely human, whereas someone who started as a fire elemental has the same problem with looking like a fire elemental. Demons nurture themselves on the memories and emotions of human beings. While they are capable of ingesting normal food it does precious little to feed them. Taking away someone's emotions or memories will, to some extent, feed the demon and make it more powerful. It is, however, much more limited in scope than the power made when creating another demon. It has been noted that demons have a great aversion to salt. To the extent that some people believe that eating salty foods will prevent you from being possessed by a demon. Salt will force a demon to take a physical body instead of an incorporeal one, as well as leading to numbing pain by mere proximity. Demons are capable of crossing lines of salt, despite what many believe, but the strain of doing so is generally not considered to be worth the effort.
Demons are never born, demons are not capable of bearing children. Through the co-operation of a succubi and an incubus they are, however, capable of creating a Cambion. A Cambion rarely comes out as anything more than a normal human though, they are often likely to be heavily affected by the Wyrd and are usually Sensitives. They will always kill their mother during birth, however and they generally end up being misshapen and ugly to look at. Exactly why demons occasionally create Cambions is unknown, they seem to serve no particular purpose besides being reviled by the local populace.