Monster Mythology Thread - All things monster in D&D and PF

[Yora]

Since the Planar Questions thread is Planar things only, and not everything is an outsider, let's start a new thread. Everyone is very much invited to ask about creatures and add any information they have to the creatures being discussed. Just post the names of any new creatures you want to ask about in bold, so people skipping over the posts can easily spot if there is a new one being discussed to which they have something to add.

The one, or actually two creatures that currently have my interest are the Dark Creepers and Dark Stalkers. I consider making them one of the Underground races for the setting I am working on, in which the Underworld is both a place below the worlds surface and the plane of aberrations. They might make a good servitor race, but that's as much as I have so far, and I was wondering if there is anything more to them than their stats and the fact that the Dark Stalkers are the leaders. Has there ever been anything about their culture or any goals or connections to other creatures?

[Deadline]

So is this specifically about in-world mythology, or to discuss where the monsters you find in the monster manual came from in real-world mythology and folklore? Because there are very few original monsters in the game.

[Yora]

My idea was more about where the creatures first appeared in, in what context, and how they were later expanded and implemented in settings and adventures.

For Dark Creepers, all the information I found in the PF bestiaries says that they live underground, wear black, sometimes come to the surface at night and... then what? :smallconfused:
They are not ghouls or demons and they are Chaotic Neutral, so they shouldn't go on a murder-spree. But what do they actually do.