Ranks for a Cult of Tharizdun

So, I'm currently running a campaign where a celestial being was recently corrupted by an artefact of Tharizdun, and has dominion over a city, bending it to serve the Chained Darkness in hopes to free him. However, I suck at coming up with cultist ranks.

Most of the cultists are simply foot soldiers who obey and don't ask questions, being imbued with a small bit of Tharizdun's power (and madness). Any suggestions?