Oh, apparently someone called "Godfry" was ruling as Elden Lord before Marika. That's the demiurge, probably.
The game's world design and aesthetic seems to be influenced by medieval European folklore, which is wonderful. But, of course, they couldn't help themselves and stuck in a bunch of gross bodyhorror monsters and general weirdness, not to mention the nihilistic moral ambiguity of the situation.
Also, too many sushi creatures wondering around. Giant land-dwelling crabs, lobsters, octopuses, shimp people, is the ocean closed for renovation? Gtfo, sea bugs.
FromSoft games are only european in aesthetics. The fundaments of everything are closely tied to asian and japanese folklore and philosophies. Plus Berserk (which was the same).
Those philosophies in Elden Ring are not eastern though, which is why there's a chance they were Martin's idea. He may have looked at Dark Souls style of "lore" and decided to come up with his own version of it.
According to Myazaki all the lore comes from Martin what Myazaki did is write the actual text in the game, which is evident since a lot of it is intended to guide the player and is also poorly written or poorly translated depending on how you want to look at it. One of the reasons the Souls are so cryptic is that the writing is confusing merely because it is kind of awkward. Once you know what the text is actually saying, you'll see the meaning is actually quite unsubtle and blunt, sometimes by design (like those white ghost guys, the only purpose of which is to give game clues).
In Souls, it is the visual story telling that's actually very good the text is often out there, which again could just be a translation issue. It's clear Myazaki wrote this stuff in Japanese then handed it to someone else to translate it.