The Cult of Violet Shadows here don't have an backstory beyond "sinister demon-worshipping cult who think human sacrifice is neat" but they sure are popular despite that.
I've been using them for all manner of random humanoid nasties in the McCullough fantasy games for a while now, and they're even been my crews for a few games of Frostgrave and Ghost Archipelago.
Many of them are lightly converted with hand and weapon swaps and the odd bits and pieces from other kits.
I went pretty light on ranged weapons, which turned out to be a fortunate choice when second edition came out and put serious limits on how many shooters you could have in Frostgrave.
Since they were also seeing use as my own crew now and then, I made up a few oddball figs for that purpose. They've also come in handy in a few TTRPG games as boss monster encounters with the regular grunts as minions.
Here we've got a Summoner College wizard and his apprentice, as well as a zombie for some casual necromancy. I'm particularly happy with the eerie lantern the boss has stuck on the end of his "staff" there. The bit actually comes from GW's old Mordheim human sprue, which is sadly out of production after its contents were removed from Age of Sigmar with the release of the Cities of Sigmar book.
And here we have two models (left and right) to swap in when we manage to cast Possess successfully, and a third that hits the table as a summoned minor demon. I find it's useful to have variant figs for Possessed soldiers so the opponent doesn't forget which models are currently hosting demonic horrors, and the unified look of everything suits my fancy more than random models. Most of the conversion parts are leftovers from Wargames Atlantic's excellent giant spider kits, which gives you a plethora of extra limbs.