Demon is a generic name for any non-human being who is mystical in nature, superhuman in power, and inclined towards acts of evil. The distinction between "demon" and "god" is somewhat blurry. While gods tend to be more benevolent in nature than demons, there are also evil gods. While gods tend to be objects of worship more often than demons, there are also demons that are worshipped. Gods and demons alike tend to dwell upon extra dimensional worlds. Gods and demons alike have greater mystical powers than normal humans beings, and have trafficked with humankind.

The major distinction between god and demon would appear to be that gods in general are a slightly more evolved life form than demons. Demons tend to be a parasitic form of quasi-mystical superhuman life, requiring sustenance of some sort (generally "souls" or life essences) from lesser creatures (like man) in order to live. Gods, on the other hand, who exist without preying upon lesser creatures. While most demons are born as demons, it is possible for a god to physically degenerate into a life-preying demon.

There appears to be three major types of demons. The first type began to existence on earth as gods. These demons, sometimes called the Elder Gods because they were the forerunners of the more anthropomorphic gods of later ages, were closely associated with the Earth itself, and may have actually influenced the terrain of the Earth as it was forming. This class of demons includes Chthon, Set, Y'Garon, Gaea, and Belathauzer, and their numerous spawn. The Elder Gods, most of who were not humanoid in form, later degenerated into preying upon their own since humankind had not yet been born. With the coming of the first generation of new gods, the Elder Gods/demons were destroyrd or if they were resourced enough, managed to flee Earth's dimension. Only the Elder God named Gaea managed to escape the degeneration process and was permitted by the new gods to exist. Geae infused her godly essense into all living things and became the goddess known as Mother Earth.

Demons of the second type may also be fallen or degenerate gods, but they date from far later generations. These demons, also called devils, dwell in extradimensional realms generally referred to as "Hells," and to this day use human beings as pawns or subjects. This class of demons includes Mephisto, Satannish, Thog, Asmodeus, and Baphomet (all of whom, possibly, are actually the same being in different guises or manifestations). Some of these entities claim to be "Satan" (a Hebrew word meaning "adversary") in order to exploit humanity's belief in a single incarnate being of absolute evil. The "real" Satan (if such an entity exists) has not yet been seen in any account. Even those human beings who believe they are related to or influenced by Satan (Daimon Hellstorm, Satana, Ghost Rider, etc.) have actually been trafficking with some other demon posing as Satan. There exists a sub-class of messenger and servant who serve the major demonic rulers of the various "Hells." These beings derive from the same origin as their masters but are inferior in amassed power. Demons in the category include Zarathos, Ningal, Ludi, Dagoth, D'Spayre, Allatou, and veritable hordes of lesser-known creatures.

Demons of the third types are also extradimensional in origin but are non-humanoid in form and alien in motivation. Some of these demons have happened upon Earth at some point in their existences; others have remained in their own realms awaiting discovery by dimension-travelers and sorcerers. Demons in this category include Shuma-Gorath, an enormous multi-tentacled slug-like creature that preyed upon humanity in prehistory, the N'Garal, a race of demons who are the extradimensional spawn of one of the Elder Gods who escaped Earth's demon-purge of eons ago, and the Undying Ones, another race of demons who originated extradimensionally.

There are also a number of extradimensional mystical beings of an evil nature whose origins are so hazy that they cannot be Classified as true demons or any of the previous three types. Some are rulers of their own dimensions, like Nightmare and Dormammu, and may be evil gods. Some live in interdimensional space like the Dweller in Darkness. Others are simply extradimensional monster (Dark-Crawler, Zom, Visimajoris), mortals (Tiboro, Xander, Shialmar, Shazana), or elementals (Hydron, Zephyr, Magnum). Truly, the multiverse of dimensions, which encompasses Earth's universe, is populated with diverse beings of supernatural attributes. A demon may simply be any or anything that says he, she, or it is one.