Spoilers ahead
Well, the Ascians are the 'evolved' (or rather, 'devolved' depending on your point of view) form of the Ancients, the original precursor race of the world prior to it's Sundering, with the thirteen named 'Overlord' Ascians all taking the names of the seats they held in the Convocation of Fourteen, the Ancients' ruling body/government (the missing fourteenth member resigned their seat just prior to the Final Days, and as it turns out,
this person is actually you, aka, Azem the Wanderer, defender of the world and it's people (or rather, your character is their reincarnation and possesses their soul).
We actually do not know all that much about the Ancients' early history - there is comments made in Elpis about Etheirys originally being an "untamed wilderness" before the Ancients' civilization came along, and Akademia Aynder went into a little history of the Convocation of Fourteen, specifically the first members of several of it's seats (the first Halmarut for instance specialized in sea life and aquatic ecosystems and from then on the Words of Halmarut took that as their main specialization.).
But other than that, we know very little to next to nothing about their early history and origins, such was the destruction the original Final Days, the Sundering and the seven Calamities wrought. So where they originally came from/who created Etheirys is completely unknown (given the big revelation in EW is that there are countless other alien worlds with life out there in distant space (or rather, were), it seems that life has always existed in some form or another, regardless of how it actually formed). But I digress.