The Creator
In the beginning, there existed one being and one being alone: The Creator. Helia did not exist, nor did the planes around it. The only thing that was present was The Creator. They do not exist in the same reality as the world of Helia, but instead they exist in a state where they are in all planes at the same time indefinitely. This concept is naturally hard to understand, as the nature of an almighty and omnipresent being should be.
The reason why The Creator decided to form Helia is unknown. It certainly wasn't to be worshiped, as very few of the people who inhabit the world do not know of The Creator's existence. Only characters with extremely deep knowledge of the world, Gods, and demigods know of them. These gods and demigods have the ability to try and communicate with The Creator, but still have never seen or even witnessed a manifestation of them. If a mortal were to see or hear The Creator, they would instantly die, as knowledge is so incomprehensible that their mind would be destroyed. Luckily, The Creator doesn't interact with Helia for this to ever happen. In fact, they are so secretive that the true (and rather uninteresting) creation story is unknown to all.