In writing this, I've found a few other useful written sources. Beside Faces of Evil, I'm indebted to Tharkul Snorrson for his On the Form and Function of Devilkind,to the tiefling Kallis Tharzar for his Exultation, and to Jeff Grubb for the new edition of his Manual of the Planes. My gratitude to them.

The baatezu claim (in the Guide to Hell, a blatant piece of diabolic propaganda if ever one was) to be one of the most primal races of the planes, formed from the original split of cosmic Law into Good and Evil halves long before Chaos was even a mad dream.

Don't believe it.

Petitioners

Larvae are the lowest form that selfish, evil souls can take as they enter Avernus from the astral conduits, although the stronger-willed spirits may appear as soul shells and sometimes as ghosts. Some say larvae aren't souls at all, but only the worms of malevolence and sin that devour a soul's integrity and spirit during life. By the time death releases the worm, only a tiny shred of individuality remains.

Some larvae, or maybe most of them, were never mortal. They're pieces of the plane itself, rejected or even budded into wriggling forms of proto-sentience. The largest known of Baator's birthing orifices is called the Maggot Pit - it's like a large inland sea filled to the brim with wriggling worms near Tiamat's lair.

More important to the economy of Baator are the soul shells, petitioners shaped into tortured semblances of their mortal forms. They aren't true baatezu, of course, but neither are nupperibos. Soul shells resemble ghost-white spectres cruelly molded into pain-wracked shapes for some aesthetic or practical purpose. A soul shell in the City of Dis may have iron nails driven through its skull and hooks in its shoulders to pull a cart, combining business with pleasure, if you will. Soul shells are the primary labor force of the Hells, eternally building cities like Dis, Minauros, and Malagard and doing most everything else the baatezu don't care to. Most commonly, they're herded about by spinagons (this is true for other forms of least baatezu).

Lemures are the mouth and gate of the baatezu species, petitioners who have been melted by hellish fire. This is necessary, the baatezu say, to purge them of chaotic and altruistic taint in preparation for their true initiation into the proper baatezu race. No soul that has not undergone this melting process is considered for promotion into higher form. How long a soul must remain part of the lemure caste depends on whether or not it has a previous reputation. A lemure that was formally an imp or a successful cleric of the Lords of the Nine will obviously be promoted before somebody who was a nameless slave-trader from Sigil. Only the most evil and potent souls are rendered into lemure form at all. Even then, many are sent back to the material plane for a time as spectres or wraiths. How do they decide which lemures to promote directly to spinagon status and which to transform into undead? Perhaps they have some way of determining a soul's affinity with negative energy, but I suspect that absent a known history the selection process is completely arbitrary. The only requirement for a lemure to become a higher fiend is for it to be physically tougher than the lemures around it. Because the melting process leaves a soul without intelligence, that's about the only distinction there is.

Nupperibos technically rank higher than soul shells and lemures, though that doesn't mean they get to boss them around or anything; they're as mindless as the larvae that they grow from. It doesn't mean they're stronger than the lemures either: most are actually a little weaker. What it means is that they're slightly more magical than lemures are, and they tend to be a little rarer (that there's only so much room at the top is a fundamental baatezu law). When they get too common, they're melted down into lemures (seeing as they've already proved themselves far stronger than most larvae) or sold to the yugoloths, who, as they are observed to fear their potential as much as the baatezu high-ups do, can be trusted to consume them. The largest nupperibo slave market is called Stenching Evil, the City of Revulsion (so-called because of the large local population of vaporighu and mephits from Gehenna). It's located in Avernus where Pyriphlegethon, the River of Boiling Blood, flows into the Styx.

There are actually two kinds of nupperibo. The kind most see is entirely faceless and featureless, looking like a star-shaped blob of boneless flesh. More rarely, you can pick out one with vague hints of eyes, ears, fingers or mouths - whether this means it's evolving into something greater, or if it just means the larva it came from was once a mortal soul instead of a stray piece of evil drawn out of the substance of the plane is something I don't know. Sometimes a nupperibo is the reborn spirit of a powerful baatezu killed off-plane. These belong to the first type, never having any distinguishing features at all.

Imps

Imps are made from larvae. They can also be rendered from other petitioner types, with more difficulty. They can't be made from true baatezu because their souls are already too defined, having been hammered into definite shapes with the impurities burnt out. Larvae are still souls in their raw form, and they can thus be made to bond easily with the souls of mortals.

The spells or rituals the baatezu use to create imps are unknown. In fact, there's a theory that the baatezu don't actually make the imps themselves - that larvae transform into imps as an automatic part of the spell used to call them. Whether or not this is true, the baatezu definitely train imps themselves. There are schools run by Furcas' Ministry of Mortal Relations where baatezu (mostly erinyes, with kocrachons to provide inspiration) train imps to do their duties. There are even, supposedly, enslaved mortal wizards and sorcerers for the imps to practice on.

Fortunately, most imps aren't terribly bright. They do their best to corrupt the mages they serve and make themselves the masters, but rare and exceptional is the imp smarter than the wizard who summons it. Those who do succeed are of course rewarded, and those who fail badly are destroyed without remorse, but the most useful service an imp provides is to create contacts between powerful mortal mages and devils better able to tempt them and guide them into baatezu plots and goals: red, blue, and white abishai; erinyes and even mightier fiends. Occasionally a baatezu will even disguise itself as an imp, answering the summons in its place.

Naturally, anyone who willingly bonds their soul to an imp familiar is owned by Baator forever.

Least Baatezu

Spinagons are the first true baatezu form, a lemure's chance to think and reason. Some are quite cunning, either due to some innate quality of the soulstuff from which they were made or perhaps an irregularity in the crafting process. This is rare, though; a spinagon is intended to be a messenger or information-gatherer, or a herder of petitioners. They sometimes act as escorts for imps, too, but most imps are expected to find their own way about.

A rumored alternate spinagon form is the plague devil, which launches disease-laden spores instead of spikes.

Herlekin are another form of least baatezu. They're strong warriors who are sent into battle after the cannon-fodder have already exhausted the enemy, so few live to see them. From a distance the tailed, hairy creatures might look like barbazu, though they're smaller. They are sent in response to summoning spells with the express hope that they'll create as many tieflings as they can before they're banished back to their home plane; most of the goat-legged tieflings you'll see have herlekin blood. Flocks of imps, mephits, and spinagons occasionally tease and torment them before flying away, but virtually any other baatezu can defeat one in battle - if it was ever encountered alone. More commonly herlekin march in broods and packs. They're most common in Avernus, though they make up a large precentage of the populace up to the fourth circle, with lesser numbers beyond. The lesson the herlekin caste teaches those who experience it is something like: It is through cooperation, determination, and the corruption of others that the baatezu race shall triumph.

How my father missed listing them, I don't know. Perhaps part of his text was damaged, or maybe they're less common than my experiences have led me to believe. As prone to wild rage as they are, superior baatezu permit few herlekin to enter Sigil, and they're never allowed in Ribcage. The only places you're likely to find them are the Blood War front and the wrong end of a summoning spell.

Ice stalkers: it was this wretched breed that finally found my father. As Tharkul Snorrson pointed out, they're excellent trackers - probably the best in the Hells except for the eager-nosed hell hounds, and better even than them when they're in cold environments, and across water and void. They're made from spinagons and retain that other least baatezu's spiny nature. Most serve as the eyes and ears of the gelugons in Caina, though they've been spotted elsewhere, especially in the colder Blood War battlegrounds. By being selected to become an ice stalker, a baatezu is taught: Even in the most desolate regions lie treasures important to the Cause.

Lesser Baatezu

The most lowly form of lesser baatezu is the abishai, who are often nothing more than the least intelligent spinagons and herlekin who happened to have survived the Blood War long enough to merit a middling promotion. The most lowly of the abishai is the black, who have little magical potential. Anything they offer the mages who summon them must be given to them by fiends with more talent than they. The goddess Takhisis sends the spirits of black abishai, combined with the magically corrupted egg of a brass dragon, to create lowly baaz draconians. It seems that the memories and specific magical powers of the abishai do not survive this process, but the baaz is still a creature of great evil.

Next is the blue abishai, which is slightly smaller than the black, but tougher and more knowledgeable. Their sour smell is mingled with a hint of ozone. It's as if the abishai are compressed as they go up in rank, each caste smaller than the last but at the same time more capable. Their skin is so dark they are often mistaken for black abishai. Blue abishai spirits are infused in the defiled egg of a copper dragon to create kapaks draconians.

Green abishai are subtler than their blue and black rivals, using sorcery as well as muscle to accomplish their goals. Bozak draconians are made from green abishai spirits and a now-cursed egg once laid by a dragon of bronze.

After that come the red abishai. While green abishai are hunters and scouts - the rangers of Baator, if you will - red abishai stride the line equally between sorcerer and soldier. These baatezu are entrusted with more magic than lesser forms, and are often sent to tempt mortals on the material plane. They're capable of teaching spells to sorcerers and witches, and are usually accompanied by one or more imps. Their sour odor is mingled with that of sulfur. In a way, their function is similar to that of mortal blackguards, and they often work with them. Their spirits and the sadly corrupted remnants of a silver dragon's egg create sivak draconians.

The mightiest of the abishai castes, the white abishai, are also the smallest. White abishai are capable in combat, but they concentrate wholly on their considerable magical gifts. White abishai are the headmasters of baatezu-run schools of sorcery, teaching magic to abishai, imps, and mortals alike. I understand that the egg of a gold dragon, charged with fell magics, is filled with white abishai spirits to create aurak draconians.

Those blue or black abishai who excel in combat and not much else are promoted to barbazu status. Barbazu are much like herlekin in temperment, and most were herlekin who did well in Blood War fighting. Takhisis once used them to make traag draconians, but they turned out to be too undisciplined, causing the project to end in failure and forcing her to use the five abishai castes instead. Barbazu often seem to be far stupider even than the castes below them; this is because combat ability is valued far more than intelligence in determining canidacy for barbazu status, so that even the dimmest of herlekin stand a good chance if they fought extremely well. Those baatezu who were of even average intelligence and fought just as well are rewarded with chamagon, hamatula, or kere status instead.

Kocrachons are considered to be equal in rank to the barbazu, but they've taken a very different path. Those baatezu who earn promotion to kocrachon status have learned subtlety and something of the art of emotional manipulation; thus, they were all red or white abishai, or exceptional spinagons. Kocrachons have the ability to surgically change the very nature of a being's soul, and for that reason they're used in all promotions that don't involve the Pit of Flame. Kocrachons are common as torturers in Dis, and they're found as deeply as the icy circle of Caina, serving under the gelugons for the amusement of the Lord of No Mercy.

Bulugons live only in Minauros, where they crawl through the swamps and rain feeding on everything they see. They also get to the Prime when they're able, collecting tribute, devouring villages and so forth. The lesson of the bulugon: Take what you can, when you can, and get out. The bulugons are created by the avaricious Lord of the Third instead of by the Dark Eight. They often speak in riddles and rhymes, as their lord does. Because bulugons serve Minauros instead of the race as a whole, transformation to bulugon status is considered a demotion reserved for particularly greedy fiends (normally spinagons, lower-ranked abishai, barbazu, and hamatulas, depending on their merit). Of course, the Lord of the Third considers it a reward for the same traits. Consequently, bulugons are looked down upon as little better than beasts by baatezu of other layers, though they're actually quite intelligent and tend to be both wealthier and more resourceful than is average for lesser baatezu. Bulugons will rarely accept promotion to anything less than erinyes status, though of course they're quick to latch on to any better opportunity that comes their way.

Hamatulas were thought to outrank osyluths: this is incorrect. It is easy to see how my father made the error, since hamatulas are singificantly tougher than the slender devils of bone, but osyluths tend to be significantly cleverer and they dwell in deeper circles of Baator. The largest number of osyluths live in Stygia, where they police the subversive tendencies of the amnizu, the loosely governed city of Tantlin, and the chaotic taint the river Styx brings from other planes. Osyluths also live as deeply as Maladomini policing the other ranks both above and below them (assisted, naturally, by secret police within the other castes). I assume that the layers of Caina and Nessus rely entirely on secret police to root out traitors and keep the devils on task (and, of course, the dreaded ashmede). Hamatulas usually dwell no deeper than Phlegethos, and they are more easily manipulated and bluffed (though it's wise to not count on being able to do this). Only the cleverest and most loyal hamatulas are rewarded with the rank of osyluth. Osyluths who serve well can usually count on becoming narzugons, although it's whispered that the best of them become initiated into the Faceless. Stygian osyluths who show a superior knack for treachery are invited to become amnizu.

Those hamatulas who show great success in patrolling the first four of Baator's circles but either too little or too much imagination sometimes end up as members of the bizarre oubliette caste. Oubliettes are little more than mobile mounts for the cruelly captured souls of the incorruptibly chaotic or good. A strike force of erinyes or narzugons brings the massive, four-legged beast along and fuses the severed head of one of Baator's foes onto the oubliette's tentacle. The oubliette than wanders the Nine Hells indefinitely, hoping to drive its passenger insane or even lawful evil by the sights it witnesses, and in the meantime preventing the soul from strengthening the upper planes or the planes of chaos. This was the fate of my father, and it is for the sake of his soul that I always return to the pits of darkness. The lesson of the oubliette is this: The full contemplation of the Nine Circles of Baator in all their splendor can only strengthen us, and weaken our foes.

Chamagons are built to fight in the Blood War as infiltrators and saboteurs. They're promoted from barbazu (and sometimes abishai, spinagons, and herlekin) who show a knack for stealth. They work to appear suddenly from nowhere, sending the already disordered ranks of tanar'ri into complete anarchy. The lesson of the chamagon: Encouraging Chaos in your opponents will aid in the ultimate triumph of Law. Chamagons are a fairly new caste, having recently been developed in the Pits of Phlegethos. The most reliable chamagons are selected to become hamatulas and keres.

To be considered for the rank of erinyes, a baatezu must serve as a kocrachon and learn thoroughly the mysteries of agony in the School of Pain. A talented erinyes knows pleasure and pain equally, and knows when to use both for the best effect in condemning mortal souls to the baatezu's ministrations. Some scholars even classify erinyes as punishers, so clever are the winged sisters at using guilt and pain to turn mortals and whole mortal communities to the dark side of Law. Exceptional erinyes may also utilize their talents in commanding whole communities, as Mysdemn Wordtwister does in Grenpoli and Aurach the Fair does in Automata. It's these erinyes who are selected to become consorts to pit fiends, and even pit fiends themselves, bypassing the intermediate ranks.

Asakku are serpentine tempters who work for the Hag Countess of Malbolge, Baator's sixth circle. Thus, like bulugons and amnizu, they are somewhat outside of the mainstream of the baatezu hierarchy, and transformation to asakku status is both a reward and a punishment. Because the Lord of the Sixth has a special love for impressionable, imaginative mortal children (as did her predecessor), the asakku make younglings their special target. Most of them were erinyes before being chosen by the Hag; they can expect to be promoted (or is it demoted?) to narzugon or even cornugon status if they serve well, although like erinyes they often decline in order to retain their unrestricted access the material plane. The asakku's serpentine form, besides being a convenient shape for crawling through the scattered rocks and boulders of Malbolge, is supposed to be a response to the celestial couatl race, which the countess considers to be either her special foe or most secret ally, depending on who you ask. The lesson of the asakku is: Seek out the enemy at its source, where it is most vulnerable. By mastering the past, you master the future. When not on a mission, asakku bask in heat of the metal fortresses that dot the layer, serving either as minor nobles beneath the fortresses' mistresses or as mistresses themselves.

Pain mistresses are drawn from the ranks of the erinyes and kocrachons, and continue their work of torture in controlling modified mortals (or, occasionally, modified lesser baatezu) called painshriekers and strigae. The prehensile pinchers of the kocrachons are replaced by massive fighting claws or even more massive grabbing claws. They also have the ability to polymorph themselves into mortal form, infiltrating other societies. The lesson of the pain mistresses: It's wise to be able to take what you dish out, but it's better if you can enjoy both. Also: Suffering brings clarity to the baatezu race, even as it clouds the perceptions of our prey.

Keres are promoted hamatulas, abishai, barbazu, herlekin, and chamagons. They do nothing but fight, but they do it well. Those erinyes and pain mistresses who have been determined to be worthy of some kind of promotion, but less talented at emotional manipulation than their sisters often become keres. Their lessons are pretty much the same as the barbazu's, plus this: It's best to follow your strengths. I've heard that keres were the special minions of the previous Lord of the First, and that because of their arachnoid forms she was called Queen of Spiders, a title that angered the demon queen Lolth. The warlord Bel has not attempted to assume any similar name, but it seems unlikely that such a tireless Blood Warrior is overly concerned with what a tanar'ri might think.

Narzugons are the baatezu cavalry, promoted from barbazu, chamagons, osyluths, and especially talented spinagons or herlekin. They ride nightmares and infernal steeds through the blasted plains and night air of lower planar battlefields, and occasionally even the Prime. They accompanied the oubliette that killed my father. Their lesson is: Rely on lesser beings to help you, and play off the fears of others.

The Faceless are baatezu assassins. Not the ordinary kind, which are simply modified versions of the standard castes, but an elite secret society with an extremely specialized form. They're so secret that I know almost nothing about them, except that I strongly suspect that like most baatezu assassins, they can turn invisible. I don't even know if they're really lesser baatezu or something greater. They keep themselves hidden even from other devils, appearing only when they're offered work, or so I'm told.

Greater Baatezu

Greater baatezu include cornugons, ashmede, amnizu, gelugons, paeliryons, and the great and terrible pit fiends.

Amnizu, the wardens of the Styx in the First and Fifth Circles, are most often promoted by Prince Levistus from those osyluths who show a superior knack for treachery, guardianship, and spycraft (though occasionally even spinagons have qualified). This gives them a noble status among the baatezu and access to great armies of herekin, ice stalkers, and abishai - even erinyes spies and consorts - but it means they live in fear of the osyluths and the pit fiends who command them. More, amnizu have to be "demoted" to the rank of cornugon before they can advance to pit fiend status themselves (of course, few ever do). Some amnizu hope to be drawn into the ranks of Levistus' nobility directly, skipping the intermediate ranks of greater baatezu, but the King of the Proud has not seen fit to do this as yet. Perhaps he fears the consequences of subverting the hierarchy in this way.

The ashmede are the special hounds of the Dark Lord. Promoted from the ranks of the erinyes, keres, narzugons, and the Faceless, they leave the pits of Nessus only on important errands of destruction. Where an osyluth might teleport an abberrant baatezu into the Pit of Flame, ashmede will swoop down on it and chop it to bits, bringing its eyes back to the Dark Lord (or perhaps his representatives, such as Martinet) for his examination. The lesson of the ashmede caste is the lesson of Baator itself: Fear ye the Overlord of the Pit, for he is vast and unstoppable. After serving their master well for thousands of years, an ashmede may have earned promotion to the rank of pit fiend.

The paeliryons are special creations of the Dark Eight, shaped by the request of Baalzephon specifically to better serve the Ministry of Supply. Since the first paeliryons have appeared, some have been able to find new assignments elsewhere, either for one of the other ministries (they especially seem to thrive in the Ministry of Intelligence), or on their own in places like Tantlin, Jangling Hiter, and the City of Man.

Paeliryons work from the shadows, through many layers of inferiors. From their secret positions of power, many effectively outrank even pit fiends. They are drawn from the ranks of those erinyes, amnizu, and gelugons who have proven themselves masters of intrigue, ready to learn the lesson of the paeliryon caste: Subtlety is all. If they so much as see your face, you have failed.

The gelugons who dominate so much of the Eighth Circle are somewhat of a mystery to the lower rungs of the infernal hierarchy. What are their duties, so integral that all pit fiends spend some time among their ranks? Some guard the Pit that leads to darksome Nessus, and some patrol the rest of icy Caina. Many, occasionally in modified form, battle the tanar'ri on the Blood War front. Some serve the Lord of the Eighth as minor nobles in his court, some serve as ambassadors to other layers, and others direct squads of ice stalkers and guilds of kocrachons. Some appear in polymorphed form as spies throughout Baator and on other planes. A small proportion of them are stationed in Stygia by the Dark Eight to keep a watch on Levistus and his amnizu.

But the primary purpose of the ice devils is simply this: perfection. The cold wastes of Caina, with their desolate, featureless terrain, are thought by Zaebos of the Dark Eight to be the ideal environment in which to develop complete clarity of mind and singularity of purpose, and so he treats the layer as the flip side and complement to the purifying Pit of Flame: a purgatory in which to test the spirits of those who would rise higher. A gelugon must serve for 777 years without a single error; most must repeat the term many times before getting it right. Some give up first, defaulting to the ranks of the Lord of Maladomini. It is the duty of Nexroth and Hutijin, and their subordinate pit devils, to monitor the gelugons' progress and report it to Zaebos' Ministry of Promotions. The ranks of ice devils and ice stalkers are filled with spies and moles to aid them in this task.

Those pit fiends who were promoted directly from erinyes or ashmede status are sometimes not so clever as those who struggled long as cornugons and gelugons. These seldom last long in the cutthroat society of Nessus, and either retreat to milder circles of Hell or die. This does not change the fact that some relatively dull pit fiends (still geniuses by human standards) do dwell in Avernus, Dis, and Minauros, far from the ranks of the arrogant and brilliant insectoid ice devils. I believe there are no pit fiends in the fires of Phlegethos who have not spent a great deal of time in the circle of ice.

Noble Baatezu

Nobles are those baatezu who work directly for the Lords of the Nine, outranking even the Dark Eight and little concerned with the operation of the hierarchy and the Blood War. Most have unique shapes, reflecting their unique duties to the lord of their layer.

Malphas, Amduscias, Goap, Mortifer, and Malgrin: These nobles serve Bel, and are thus an exception to the general rule that nobility doesn't interfere with the Blood War. They spend most of their time rallying the armies of Avernus.

Adramelech, Martinet, Phongor, Bune, and Alastor: These nobles serve the Dark Lord of Nessus directly, and spend much of their time supervising and even, in some cases, overriding the Dark Eight. Alastor is a pit fiend, said to be the greatest of his kind.

Some baatezu are minor nobles, ruling towns and fortresses in the name of the Eight. Often they are erinyes, cornugons, and amnizu.