If you're at all familiar with the Great Wheel multiverse of Dungeons & Dragons, you've noticed it has a tendency towards symmetry. The Lower Planes have Fiends, the Upper Planes have Angels, Mechanus has Modrons and/or Inevitables, Limbo has Slaad... so, what bout the Outlands? What kind of extraplanar being exemplies the metaphysical concept of absolute neutrality?
The answer, according to Planescape, is the Rilmani. Sadly, given this was the edition in which True Neutral was synonymous with Stupid Neutral, Rilmani are basically dedicated to "preserving the Balance" by constantly fucking up things for every one of the four alignment axis's, based on their own judgment as to when one is too strong.
|The inhabitants of the Planes of Planescape|
|Upper Planes:||Aasimon - Angels - Animal Lords - Archons - Asuras - Eladrin - Guardinals - Lillend|
|Middle Planes:||Formians - Githzerai - Inevitables - Marut - Modrons - Rilmani - Slaadi|
|Lower Planes:|| Alu-Fiends - Baatezu - Bladelings - Cambions - Demodands - Erinyes - Hags |
Hordlings - Imps - Kytons - Marilith - Succubi - Tanar'ri - Yugoloth
|Transitive Planes:||Astral Dreadnought - Githyanki|
|Inner Planes:||Azers - Elementals - Genies - Grues - Mephit - Salamanders - Sylphs|
|Sigil:||Dabus - Cranium Rats|
|High-ups:||Archangels - Archdevils - Archfey - Archomentals - Demon Princes|