These are the insane humans who through seances, reading arcane books of anchient and forbidden knoweledge, or even through direct contact have turned to serve the Aged Ones. Their sole purpose is to bring the Aged Ones or even Ab-Juhadah itself into our sphere of existence in order to destroy the Gods once and for all. However, their madness prevents them from fully realizing the error of their ways, for once the Aged Ones have been unleashed, they will not take any side, but destroy randomly and mindlessly.

Pretty much any being with human-level intellect can join the various cults listed elsewhere. However, that cult must fit with that character/race's themes, and so some cults are much more appropriate than others deoending on the race.

Requirements for humans usually calls for them to have been exposed to the Aged Ones directly or indirectly long enough to go insane. Thus, no sane human can join unless they become insane first.