tanari are just one "type" of demon. What are all the rest in the infinite Abyss?

[Gez]

Along with the gacholoth and guardian yugoloths.

Gacholoth maybe, but guardian yugoloth? No. They were only yugoloths because of an over-enthousiastic Find&Replace feature. (The same way that, previously to the publishing of the FRCS, you had one or two cleric domains in the RPGA FR Guidelines document that had the "Xvim" spell at first level. You had to keep the secret on Bane's resurrection, so every single instance of "Bane" was replaced with "Xvim", even when it didn't make any sense.)

Guardian daemons were called guardian daemons using the ancient greek meaning of daemon (spirit) rather than the D&D meaning of "neutral evil denizens from Gehenna and Hades". Least GD weren't even evil in alignment, and the more powerful ones only had evil tendancies.

They don't make sense as yugoloth.

 

[dead]

Which adventure? (I'm sorry to say I never fully read the Tales... only skimmed through it as I wasn't running Planescape at the time)

The baatorians are mentioned in Tales from the Infinite Staircase. The Kyton leader (Quimath?) has one locked away in his stronghold. So probably the last episode in that book.

 

[Malar]

about them demons

I think the AD&D system was pretty clear on who was who. Tanarrii and Baatezu fight each other endlessly and the Yugoloth have no standing point, but sell their services to the highest bidder. It was excellently explained in Monstruous Compendium - Outer planes. The prime concern of all Tanarri and Baatezu is of course the Blood War, but many of the bigger lords have their own agenda.
I happen to have a (complete?) list from that particular compendium including xp values:

Tanarri (CE)
manes 1000 least
dretch 8000 least
rutterkin 12000 least
cambion 13500 lesser
alu-fiend 18500 lesser
nabassu 22000 greater
bar-lgura 22500 lesser
succubus 29000 lesser
chasme 30000 greater
vrock 37000 true
hezrou 39000 true
babau 42500 greater
nalfeshnee 43500 true
glabrezu 44000 true
marilith 45000 true
balor 46000 true - True leaders behind the Tanarri blood war effort.
molydeus 53500 guardian - 'Police' of the blood war. If some other Tanarri abandons the cause he is hunted down by the Molydei. This concerns even Balors.

Baatezu (LE)
nupperibo 65 least
lemure 120 least
spinagon 7500 least
hamatula 23000 lesser
abishai 23500 lesser
barbazu 23500 lesser
osyluth 24000 lesser
erineyes 29500 lesser
amnizu 32500 greater
cornugon 36500 greater
gelugon 39500 greater
pit fiend 57500 greater - Rules supreme over the lesser Baatezu and forces them into fighting in the blood war.

Yugoloth (NE)
dergholoth 25500 lesser
hydroloth 26500 lesser
yagnoloth 26500 lesser
mezzoloth 40500 lesser
piscoloth 40500 lesser
arcanoloth 49500 greater - Negotiators
nycaloth 66500 greater
ultroloth 84000 greater - True leaders, seldom seen.

Also, there are other fiendish creatures, like the Slaadi that could be considered a race, some other groups like Geheleths (if I recall correctly), and some other individual demons that do not belong to any group like Bebiliths.

 

[Incenjucar]

Exemplar: Outsider that exemplifies alignment for a plane. Aka Celestials, fiends, modrons, and slaadi.

Fiend*: Exemplar creature forged of baernoloth action, or a baern itself. Includes Tanar'ri, Baatezu, Yugoloths, and Gehereleths.
* This is an effective definition, but not, I wager, an intended one.

Demon/Devil/Daemon: Outsider on respective lower planes. Certain oni may be included here, for instance (some others are probably giants, etc). Fiends are as well.

Lower Planar Creature: Anything from the lower planes. Includes non-outsiders, like the khasta.

Here's the fun trick here: It can be argued that, while they are EFFECTIVELY so now, the fiends are not the true evil exemplars (except the baern, mayhaps). It could be argued that the hordlings, ancient baatorians, and whatever the tanar'ri replaced, are the true exemplars. Assuming exemplar even has meaning beyond a title granted by presence, in which case, it's a fluid thing, and changes over the eons.

Remember, according to yugoloth lore, all of the fiends (as I defined them here) are constructs, and only the baern are actually natural beings. The fiends are, essentially, the army of the baern used to knock down the other native races, which might have had potentially equal power.


Also a note I feel I have to add to Shemmy's mention of the older ancient baatorian -- it was ASLEEP. We have no idea if it looks like that or is that well-defended when awake. It could just have a really great defense when snoozing, but be around a pit fiend's power when awakened, but able to attack actively. I just feel the need to keep that in everyone's mind, lest we start assuming that the ABs are all uber slugs or nastier.

Another thought: Since so many things evolve from the larva.. perhaps the baern did too. Perhaps the draining devices in the Waste are what keep them from being more populous.

 

[Savage Wombat]

Just to add to the ancient Baatorians discussion:

If you think about it, this is the ultimate expression of the Lawfulness of their nature. Nobody "just naturally" becomes a Baatezu - they have to be forced, by creatures more powerful than they, into following their system. Nature and personal choice have nothing to do with it - you follow orders or you are destroyed.

Planescape had a lot of subtle commentary on alignment through concepts like these.

 

[Alzrius]

Guardian daemons were called guardian daemons using the ancient greek meaning of daemon (spirit) rather than the D&D meaning of "neutral evil denizens from Gehenna and Hades". Least GD weren't even evil in alignment, and the more powerful ones only had evil tendancies.

They don't make sense as yugoloth.

You seem to have missed some of the later Planescape works that explained all of this. The guardian yugoloths were created by the other yugoloths for the sole purpose of being there to soak up summoning spells, freeing the rest of the race up to actually accomplish things. The Canoloth was similarly created (can't recall exactly why).

They make perfect sense in that regard.

 

[Shemeska]

You seem to have missed some of the later Planescape works that explained all of this. The guardian yugoloths were created by the other yugoloths for the sole purpose of being there to soak up summoning spells, freeing the rest of the race up to actually accomplish things. The Canoloth was similarly created (can't recall exactly why).

They make perfect sense in that regard.

Yep, somehow the Yugoloths managed to rig random lower planar summons to preferentially target Gehreleths first, and then Guardian Yugoloths and Canoloths to at once, both spite the 'leths and remove the chance of any actually important Yugoloth from randomly vanishing to the prime to serve a mortal.

And damn did the 'leths abhor the 'loths for that, however they did it, among massive other reasons.

They expanded upon this later with a Shator Gehreleth working to publish an expanded copy of the 'Book of Keeping' that contained large numbers of 'loth true names to bind important Yugoloths in mortal summons as a sort of cosmic revenge by the 'leths.