Fiend

A fiend was an evil creature from one of the Fiendish Planes, also called the Lower planes in some cosmological models. They were not just evil, but born of evil; primal malevolence was one of the roots of their nature, and the evil essence of the fiendish planes permeated every part of their bodies.

"There's more to their villainy than meets the eye."

- A sage of the Prime Material plane

Personality
Fiends lived long, and some had an inhuman view on time and life. They were capable of viewing a century passing by as inconsequential.

Relationships
The demons and the devils held an eternal enmity for one another as they waged the Blood War.

True Name
Every creature had a true name that made it possible for other creatures who knew it to gain control over the them. For fiends, the true name was a double-edged sword. Knowing their own true name made it possible for a fiend to rise up the fiendish ranks, something that was very difficult for fiends without that knowledge. On the other hand if knowledge of a fiend's true name somehow spilled out, it granted other creatures control over them. This control extended very far. For example, a mortal knowing the true name of a fiend could not only call it from the Lower planes to the Prime Material plane but also force it into servitude. Fiends could inconvenience or torment their rivals by helping mortals discover their rival's true names.

As mentioned above, a fiend needed knowledge about its true name to rise up the fiendish hierarchy. It often happened that the true name became different on changing form. It was believed that this was not the true name changing but some form of evolution of the true name. The core of the true name remained the same but there were some additions to it. When a mortal used an outdated true name to bind a fiend, the fiend responded to the binding. However, the control the mortal exhibited over the fiend was not complete and could have fatal consequences for the mortal.

Mortals
Mortals and the worlds they lived on were seen as useful by most fiends but this did not mean that they viewed mortals as having any intrinsic value. The value of mortals laid in their potential to be turned into fiends after dying. To do this, mortals were exposed to temptation by certain types of fiends. Otherwise, mortals were of use only as slaves, playthings, food, and mercenaries as far as the fiends were concerned. The Prime Material plane was seen as a potential battlefield due to its lack of guardian outsiders, however, it was at its most useful when used as a generator of faith. The Outer Planes were altered by the beliefs of others so when mortals started to respect or fear them, the fiends grew in power to match mortal perception, incentivizing the fiends to terrorize mortals.

History
The important event in fiendish history was the Blood War. The Blood War was an interplanar battle between demons and devils. This cost so many lives on both sides that they were forced to figure out how to refill their ranks in rapid fashion. The answer both sides came up with was to convert larvae into fiends. After they found out that larvae were what became out of the souls of evil people, they started to work towards turning mortals to evil.

Ecology
Not every creature from the Lower planes was a fiend. Only baatezu, gehreleths, hordlings, tanar'ri, and yugoloths were actual fiends in the narrow sense. In the broader sense, every outsider with evil as part of its being was a fiend.

The life expectancy of a fiend was not known. An observation about their aging process was that they did not mature. Those fiends that reproduced, gave birth to a smaller version of their species that grew bigger and stronger with time, but a fiend dying of natural causes or just growing old was never observed. Because of this, it was assumed that they were immortal. One unique feature was that they changed from time to time into a different form. However, this was transformation and not some form of biological metamorphosis.

Demons
Demons were the most widespread race of fiends. They were chaotic evil and were native to the Abyss. Tanar'ri, obyriths, and loumara were the three main races of demons, but there were many other species as well.

Yugoloths
Also known as daemons, yugoloths were manipulative, neutral evil fiends native to the Blood Rift. They were secretive and mercenary by nature.

Devils
Devils were lawful evil fiends who hailed from the Nine Hells of Baator. The baatezu were the dominant species.

Demodands
Also known as gehreleths, demodands were said to have been fashioned by one of the primal creations of Evil, exiled because of their chaotic taint. They dwelt in the Supreme Throne.

Archfiends
Archfiends were not actually a separate kind of fiend on their own, but rather a grouping of powerful, unique fiends of any of the above kinds. The most prominent groups were the archdevils and demon lords. Archfiends could be incredibly powerful, almost as powerful as true deities.

Half-fiends
Due to their magical natures, fiends were capable of breeding with most other creatures. The resulting offspring was called a half-fiend. Some such hybrids could breed true. Notable varieties of half-fiends included cambions, and draegloths.

Other Fiends

 * Achaierai : Creatures that looked like large, flightless birds with four legs.
 * Hell hounds : Fiends that looked like large, powerfully built dogs with rust-red fur, red eyes, and black teeth and markings.
 * Barghests : Shapechanging fiends native to Gehenna, barghests naturally resembled large, goblin-wolf hybrids with orange eyes and blue fur.
 * Larvae : Also called soul larvae, larva were the fiendish remnants of evil mortal souls.
 * Night hags : Merciless, horrible humanoid fiends with black skin, red eyes, skeletal bodies, clawed hands, and horns. Night hags also possessed powerful magical abilities.
 * Nightmares : Neutral evil fiends that appeared as large black horses with flame in place of a mane and tail, and flaming hooves.
 * Maelephants : Large, humanoid fiends with clawed hands and elephant-like heads. They were often employed by more powerful fiends as guardians of treasure.
 * Rakshasas : Powerful, sorcerous fiends from the lawful planes with animal-like heads and backwards hands.
 * Vorr : Bloodhound-like fiends that hunted in packs.