Tanar'ri are the chaotic evil supernatural badguys, in 2nd Edition Dungeons and Dragons. After TSR got their new CEO Lorraine Williams and Gary Gygax left in disgust, the company decided that nutcases like Jack Chick and Patricia Pulling had to be pandered to, so Williams said "no more demons, or any of that junk". In 3e they wisely decided to use "demon" again, but kept the term "tanar'ri" as a subtype of demon. Since TSR bothered to register "tanar'ri" as a trademark, you will not find this demon subtype in Open Gaming License materials like the D20SRD.
They are the archetypical chaotic evil outsiders, seeking to destroy all order and plunge creation into mad, violent chaos in different ways. They are one of the two major factions in the ideological Blood War, the other being their lawful evil counterparts, the baatezu, or devils.
Fiendish Codex II - Tyrants Of The Nine Hells states that Devils call all demons Tanar'ri for short, which is strange considering that in the same book it says that in the devils' language "only one correct way exists to construct any given statement in Infernal." and "[Devils,] except when in disguise, they find the urge to correct errors in spoken or written Infernal nearly impossible to resist." This may be a hint as to the origin of Lorraine Williams, since she also insisted on using the term "tanar'ri" instead of "demon."
Types of Tanar'ri
There are many types of Tanar'ri, one more terrible than the next. There is something of a degree of power that seperates the various demons, but this is not absolute. There are five categories that divide them however, and each group is more powerful than the ones below it.
Tanar'ri can ascend to a new form if they believe they have what it takes to do so (mainly based on how deadly it is) and can prove this to those around them. While ascending step by step though the ranks is the most common way to do this, particularly powerful or intelligent Tanar'ri can skip one or more forms.
- Manes: The lowest of the Tanar'ri and barely worth the name, Manes are a source of food and cannon fodder, herded at the enemy to tire them before the main forces strike.
- Dretches: Barely above the Manes, the Dretches are real Tanar'ri, albeit the lowest in rank. They suck up to the more powerful members of their race (pretty much all of them), and are treated as such in reply.
- Rutterkin: Vicious and despised by all other Tanar'ri, the Rutterkin are the preferred targets of higher-ranking demons for harassment, torture and murder. In return a Rutterkin will attack anything that they think can kill without much risk to them.
- Alu-fiends: The female child of a Succubus and a mortal, Alu-fiends can only be born into their rank. They are not physically powerful but they are powerful spellcasters and physically attractive, which makes them useful to the high-ups in the Abyss.
- Cambions: The opposite of their Alu-fiend sisters, Cambions are the children of a Tanar'ri and a female mortal. A major Cambion is born when the father is a Lesser or Greater Tanar'ri, while a True Tanar'ri sires a Baron or Marquise Cambion, who are significanlty more powerful than their lesser kin.
- Armanites: The centaurs and bariaurs of the Abyss. They band together as mercenary groups and hire themselves out to whoever pays the most.
- Maurezhi: These Tanar'ri have the strange ability to gain the memories and experiences of whoever they eat. They can only be created by Abyssal Lords for specific missions, but can grow to new forms as usual.
- Succubus: You know them, you love them.
- Yochlol: The handmaidens of Lolth, the Yochlol are shapeshifters who can freely change between their drow form, a spider form or that of a great mass of yellow ooze with a single staring eye. They enjoy Lolth's protection from other demons and act like it, but they'll get brutally murdered if another demon thinks it can get away with it.
- Bar-lgura: Gorilla-like Tanar'ri trained in guerilla warfare, they are brutish, dumb, slow of mind and can casually rip your arm off.
- Bulezau: Rocking a traditional Satan-esque look, the Bulezau are powerful, elite soldiers who want nothing less than murder all their enemies within sight.
- Nabassu: Gargoyle-shaped things serving as the heralds of the Abyss, seducing humanoids to the service of the Abyss.
- Chasme: Huge fly-like things that seek out deserters of the Blood War. They mostly stay out of the affairs of others to carry out their duties.
- Babau: The recruiters for the Blood War. Or rather than recruiting they press-gang other demons to fight. If they don't meet their quotas however they have to fight themselves.
- Goristroi: 20' bulls that serve as living siege engines to topple walls and crush enemies below their feet.
- Wastrilith: Great serpent-like monsters who stick to the waters of the Abyss, mainly the waters of the Styx which they can navigate unharmed. They serve as the guardians for the waterways of the Abyss, eager to devour anything that gets near.
- Vrock: Humanoid vultures that serve as elite soldiers in the Blood War.
- Hezrou: Frog-shaped Tanar'ri possess a cool, sharp intellect that allows them to perform their duties in the Blood War with precision and dedication.
- Glabrezu: The primary summoning material, they are skilled at tempting their summoners and giving them plenty of gifts of power, only to withdraw said power at the worst possible moment to get them killed and pulled into the Abyss.
- Alkilith: Oozes that can corrupt anything and anyone with a mere touch. They don't fight in the Blood War, mainly for practical reasons on account of them being oozes.
- Marilith: Attractive women with the lower body of a snake and six arms, they are the tacticians of the Abyss. They have keen minds, anticipate what the forces of Law are going to do and act upon it, much to the rage of the Baatezu who cannot understand the plots of the Marilith.
- Nalfeshnee: The judges of the Abyss. All petitioners that enter the Abyss pass by a Nalfeshnee who judges them based on their lives and appoints them a new form. At least sometimes: other times they hand out forms at random. They also determine who gets to be in charge of the armies and who gets to be promoted, demoted or removed from (as in: destroyed) its ranks.
- Balor: The dreaded kings of the Abyss, Balors are the most powerful of the Tanar'ri, serving as lords, generals and leaders, inspiring and threatening others into fighting for the cause. A mix of passion and reason, they are as intelligent and sharp as they are evil and chaotic.
- Molydeus: The only Tanar'ri within this rank, a Molydeus stands outside of the ranks of the other Tanar'ri, making sure that their kind stays true to the ideals of the Blood War. While they report to the Balors, a Molydeus will not hesitate to turn on their leader if they are not showing sufficient zeal. So in essence they are axe-wielding, dog-faced Commissars with a snake growing out of the back of their heads.
The first amongst the demons, the lords of the Tanar'ri (more commonly known as Demon Lords) are some of the most powerful, dangerous, cunning and deadly beings in existence. They attained their position by strength of arms and cleverness (mostly the former) to rule over their servants. Those who wish to challenge their lords are quickly struck down as an example and to keep the other minions in line.