Originally Posted by
Him of Many Faces
As for their hierarchy it's pretty much a caste system, where specific races are transformed into demons to suit specific needs. With enough power you can choose your own caste ofc.
-the eredar are the brains, top level commanders and strategic decision makers, as well as the elite magical forces
-pit lords are like army generals more or less
-dreadlords are kinda like the CIA, doing clandestine and hidden things, attack from the inside, etc.
-Doomguards are like a army NCO, commanding smaller legoin units in battle, as well as the primary flying forces (untill the introduction of the new flying demons in legion at least)
-felguard are rank and file troops
-felhounds arent fully sentient, and are treated more like pets/attack dogs
-the mo'arg primary job isn't fighting but maintaining their technology
the rest of demons more or less got tagged on after those were created, so they don't fill as obvious niches, most of it is just rule of cool thats later justified somehow.
satyr are kinda like dreadlords but on a smaller scale, very scheming, basically they are demonized nelfs.
succubi and those shrivannas are to seduce/trick people
imps are like your traditional trickster deamon who comes to bite you in the ass after you make a deal with him, the unwilling servant who rebels when he can, etc.
voidwalkers arent very sentient, and technically not even demons these days.