Sentient

The first mistake of the Eidolons, the sentient was the catalyst for everything that is known, sparking life, thought, land, sea, evil, good, and all else; the eidolons may have been the creators, but the sentient created.   Near the beginning of time, an Eidolon known as Erra was just beginning to get accustomed to their powers of creation, populating their home, the Praeterian plane, with simple objects and structures, purposeless and vague; easy to remove, if it wasn't perfect enough. However, soon, Erra began to get more comfortable with their fabricative powers, and in one fateful moment, they accidentally created a being with a mind of its own, Talis. When Erra realised what they had done, they attempted to destroy Talis, but lacked the power to do so, as the strength of the Eidolons was in creation, not destruction. Talis sensed the fear in their creator, and the scarring memory of Erra's attempt to destroy them never left its mind. Talis fled, although Praeteria had no-where to hide, so they used their own powers to create a mirror dimension which overlapped Praeteria, known as the Tellurian plane; Erra could not reach this plane, and they felt that their fears had come to fruition, the pristine world of Praeteria would be corrupted, marred by the existence of their own creation, the sentient, Talis.   Now in their own world, safe from the mother that tried to destroy its mistake, Talis wanted to make their world into a haven where nothing would be an accident, everything was welcome, everything had its place; after all, imperfections only made the perfect more beautiful.
Talis began laying down their world, mountains, valleys, plains, and all the other landscapes they could imagine; but unlike in Praeteria, Talis had nothing to observe their world, they were alone, so they made life; this life was no-where near as advanced, nor powerful as Erra had made Talis, since they were significantly weaker than Erra, but Talis wanted them to have the freedom to explore, to adapt, to evolve. Talis thought about how to give their life a power of its own, and they came up with a plan; Talis made another plane, nestled below Tellus, and this plane would be filled with a festering chaos, uncontrollably wild and completely unbound by Talis' command. Although this chaos was physically kept in another plane, away from the Tellurian plane, Talis deliberately let its influence reach out, infusing the primitive life with will, and the slightest drop of chaos, a soul.
  Their plan had gone perfectly, life was beginning to evolve, becoming more advanced, still wild, but effective, and most importantly, free. However, Talis underestimated the power of this chaos, which they called the abyss; the small channels that were intentionally made to allow it to influence Tellus were torn open, and the abyss begun to crawl out, decimating the world above and threatening to ruin it all. Talis instinctually thought about destroying the abyss, to preserve the world they loved, exactly what Erra had done to them. Instead, they made another plane, equal in power to the abyss, but devoted to keeping order; exerting a balancing force that kept the abyss at bay. This plane they called the cosmos, a completely serene landscape; full of spires and geometric shapes, unchanged by time, unflinching in purpose. Talis had anticipated there would be side-effects to such a brash action, and was prepared for the worst; though they didn't anticipate anything close to what those side effects would actually be.
The abyss had given life the ability to evolve, but the cosmos had given it something far more impactful, intelligence. Not too long after Talis made the cosmos, some of the first intelligent life evolved, notably, the species known today as the sobek, who dominated the lands of Tellus for many thousands of years   The loose balance of Tellus had been created, and for hundreds of thousands of years, it stayed; although, Talis began to tire from the worries and responsibilities of preserving this new world, and the fine balance of chaos and perfection, so they made a great sacrifice. To let the world thrive, truly without the control of Talis, they split themself into three beings, one to govern each plane: the Cascade, the Symphony, and the the Remnant.
With Talis being secluded to a mere whisper on the wind, Tellus was truly free; its civilisations grew, cultures developed, wars waged, great cataclysms broke it apart, all without the guidance, nor even the knowledge of its benign god. Perhaps Talis will return one day, to right the wrongs of their mother and destroy the blighted mist that Erra layed upon the world.