The Luonnotor are a secretive sect that teach that all the so called gods are but petulant children unworthy of worship, and that The One true creator will return someday to judge the whole world, including the "gods." They are right, although it is unclear how they figured it out. It was probably just a lucky guess, although Junil fears that The One may have returned in secret to make himself known, that he must have been greatly displeased with the god gods not to come to them first, and that this ma be a sign that the end is very near. The Luonnatar were persecuted for their blasphemous teachings by followers of good and evil gods alike, and probably by a lot of neutrals too. (Good and Neutral gods are loyal to The One, but they do not believe that he wanted to make himself known to humanity so they have never told their followers.) Most notably, the Luonnotar were captured by the Bannor, whose priests judged their blasphemy as a capital offense and decreed that they would be punished in the most appropriate way--by being burned alive in holy fire. They were tied up in the middle fo the town square, and a Prior cast Pillar of Fire. The flames rained down, but Junil refused to let them hurt them. They burned through the ropes but left the Luonnotar unscathed and allowed them to walk away freely. The priests of course thought this meant they were practices of serious witchcraft, so they tried to track them down to kill them again. They however managed to escape to the Grigori lands, where Cassiel gave them refuge. Cassiel also believes that only The One is worthy of worship, but he does not believe that he would want to be worshiped as worship is most closely tied to Agares' sphere and he cannot imagine The One having such a corruption. (Note that while the former archangel Cassiel has heard all the gods discuss their view of The One, he has never actually met them.) Cassiel dislikes all religion, but fears that militant atheism could become just as bad so he makes sure that all Grigori have complete freedom of religion so long as they don't use force or fraud. The Luonnatar get no special treatment. As most Grigori as refugees from religious wars, they have generally come to oppose the whole concept of religion and don't see the Luonnatar as any better than numerous other cults.
I do not believe that Luonnotar is ever used as a name for The One, the only divinity they worship.
The name Luonnotar derives from some obscure goddess that created herself out of nothing and then created the universe. I believe that an egg was involved. As in most cases where Kael borrowed a name from real world mythology, he did not borrow many other details to go with it. For instance, Danalin's archangel Condatis is female, not a male god synthesized with Mars.
The One is generally referred to using masculine pronouns, but I have trouble conceiving him with any gender but grammatical gender. There are 5 angelic names for him, and I suspect that the gender among those is not constant.