A fiend is a supernatural and malevolent being prevalent in religion, occultism, literature, fiction, mythology and folklore. From there, they made their way into Dungeons & Dragons as a malicious otherworldly creatures with many different races originated in the Lower Planes. The most widespread race of fiends are demons, who are chaotic evil by nature, and are native to the Abyss. They have no true rulers, though powerful demon lords are able to gain enough power and influence to gain control over sizable armies of demonic creatures.
The dominant race of demons is the tanar’ri. In theory, both the Abyss and its population are infinite in size. “True” tanar’ri such as the balors (probably a name inspired by Tolkien’s “balrog”) and the six-armed serpentine mariliths push other weaker tanar’ri around and organise them into armies. Demon lords and demon princes such as Orcus, Demogorgon, Zuggtmoy, Graz’zt and countless others rule over the demons of their individual layers of the Abyss (or at least they try).
The devils, of which the ruling type are called baatezu, are lawful evil natives of the Nine Hells of Baator; they subjugate the weak and rule tyrannically over their domains. Pit fiends are the most powerful baatezu, though even the strongest pit fiends are surpassed by the Lords of the Nine, or Archdevils, whose ranks include Baalzebul, Mephistopheles, and Asmodeus. Unlike demons, devils arranged themselves through a strict hierarchy.
On the other hand, yugoloths are neutral evil natives of the Bleak Eternity of Gehenna and the Gray Wastes of Hades; they are neutral to the affairs of the other fiendish races, interfering only when they see a situation that may be profitable or a potential for the advancement of their own schemes. The yugoloths are manipulative, secretive, and mercenary by nature, often acting as soldiers for deities in their own private wars, or even at times aiding both sides of the Blood War, the eternal conflict between tanar’ri and baatezus.
The Blood War is depicted as a bitter war of annihilation between the baatezu race and the tanar’ri: an absolute, all encompassing, and virtually eternal struggle, from which result the fate of all planes depend. The Blood War was thoroughly detailed in various books throughout the Planescape setting, particularly the 1996 boxed set Hellbound: The Blood War. The 4e Manualof the Planes updated it into a smoldering cold war. Its causes are lost in time, and as such, different ones have been given through many sourcebooks: from an offshoot of the primordial battles between law and chaos, continued out of violent and sadistic stubbornness, to an eternal war against the demons by a former angel turned into the original demon or even a distraction by Asmodeus to hide his true goal of usurping divine power and reshaping the multiverse.
The Overlords are the most powerful of the fiends of Eberron. They sprung from Khyber ten million years ago. These spirits, also called the rakshasa rajahs, ruled over the lesser fiends during the Age of Demons. However, the children of Siberys and Eberron, the dragons and the couatls, joined forces to rid the world of the Overlords and their fiends. The couatls gave their lives to trap the thirty Overlords deep beneath the Khyber, where they still sit today. Their former minions, the rakshasas and other fiends, have formed the Lords of Dust and seek to free them from their prisons. Only a few of these thirty are known:
- Bel Shalor, “the Shadow in the Flame”, is a fiend that almost escaped, but was stopped by Tira Miron and was trapped within the Silver Flame. Some say that he is still trapped within the flame in Flamekeep, while others think he is trapped within the petrified body of Melysse Miron.
- Dral Khatuur, “the Heart of Winter”, is a female elemental force that, upon release, would cause a new ice age.
- Eldrantulku, “the Oathbreaker”, is the spirit of discord, turning allies into enemies.
- Katashka the Gatekeeper is the overlord of life and death, and the creator of the first undead. Katashka’s first servant was the demigod Kyuss.
- The overlord now known as Levistus was imprisoned deep beneath the ice of the Frostfell.
- Malathar, The Keep of Secrets, is a cat-like fiend that was imprisoned along with the Couatl that had bound it beneath Aundair. Its essence, along with the that of the Couatl and the power of the Storm Dragon, could be harnessed to create the Dragon Forge, a weapon capable of devastating the Eldeen Reaches and the eastern Demon Wastes.
- Masvirik the Cold Sun is the Overlord with domain over the things that slither in the night. Masvirik is trapped deep within Haka’torvhak, where his servants Rhashaak and the Blackscale Lizardfolk and Poison Dusk Lizardfolk await his freedom.
- The overlord Sakinnirot claimed ownership of the continent of Xen’drik, and is now trapped beneath Stormreach.
- Shudra the Fleshrender is a fiend imprisoned beneath the of Mel-Aqatis, along with the spirit of the Couatl that bound it. Its rakshasa servant attempted to escape and free its master by stealing the body of the wife of Janik Martell. It was thwarted by the efforts of his new lover, a priestess of the Silver Flame who was able to defeat the Flesh Renderer with silver torc gifted to her by the spirit of a Couatl.
- The Spinner of Shadows is a female overlord that is imprisoned deep within Khyber, near Tarath Marad. For ages she has waited for just one moment of freedom so that she may once again spin her web of treachery. She was attended by Drow, Reavers and Hezrou.
- Sul Khatesh, the Keeper of Secrets, is the master of arcane might and mystery. Unknown to most, Sul Khatesh is trapped beneath the Arcane Congress, whispering to them in their sleep.
- Tiamat, the Daughter of Khyber, is the truest child of Khyber, and holds dominions over dragonkind. She is trapped within the Pit of Five Sorrows, where the Talons of Tiamat hope to free her.
In your campaign
When using devils or demons (or other cosmical entities), keep in mind they are much more than just monsters who lead a random encounter. Devils and demons must be actively sought after, and probably they know are being sought, so remember the mutual attention given by adventurers and villains. One way to accomplish this is to make clear to the characters that, as they observe and chase a fiend, he also observes and persecutes them. The trick is to demonstrate this to the players indirectly, so you have to figure it out. My favorite tool is given by the Chronicle of Korranberg, or the Inquisitor of Sharn: a brief news about a cruel murder after an obvious torture could go unnoticed by anyone in such a large city, until law enforcement discover according to some witnesses that the victim was physically very much like one of the heroes. Was the hero the intended victim? You can find some other useful tools when dealing with these creatures in my article “The Art of Fear”.