A few weeks ago, I created a group of eldritch-like beings for my fantasy world that a series of novels will take place in. Then I started working on a JRPG/anime themed fantasy setting, which you can watch on Youtube. During the last session, I decided to pull the eldritch beings into this new setting instead, and made some adjustments.
Origin
Previously, these beings were from a shadow or void plane. They migrated into the mortal/material plane but instead of attacking people or eating them, they decided to join them. Their new origin story is that two second-level deities, one being the god of birth rites and the other the god of funeral rites, tried to make their own group of mortals. It backfired, resulting in beings with twisted or incomplete forms, but because they did have souls, the two deities couldn't get rid of them.
Instead, they hid them in a pocket dimension, which was essentially a bleak and dark prison. Another second-level deity, the god of sowing, discovered them and set them free. The first-level deity within the same domain, nature, decreed that if these beings could live as they are, then they deserved life as mortals. And so, they live.
Appearances
Their appearances didn't really change much. They still often have tentacles that appear from their back, fangs, and horns. Their true forms are still quite horrifying, sometimes barely tangible. However, they keep these forms hidden, either because they're ashamed of them or because it's simply more convenient to look like everyone else.
They also now apply magic to help with this illusion of normalcy.
Culture
This also stayed close to the original idea. Since they had first lived within a pocked dimension shadow land, they though the mortal world was a utopia. They became enamored by food and drink, and created the world's largest, most comprehensive library.
This was a pretty fast blog entry that mostly rehashed some things, I'll admit. But I've been doing a lot of worldbuilding lately, so I'm counting this. :P