For a Will to manifest on a planet, there were 3 conditions that needed to be fulfilled.
First, there needed to be an Origin that had formed on the planet. Most Origins were randomly formed, but one could influence the formation by planting energy on a planet. That, however, would require an unimaginable amount of energy to do so.
Second, there would need to be a considerable amount of souls on that planet, each of which would influence the will of the planet to form a will.
Finally, the amount of energy on the planet had to exceed a certain level of threshold that was different for each planet based on its size.
When all the conditions were met, there was a good chance for wills to manifest on that planet.
Halios was one such will. Long ago, when the world of men was still learning to reach the pinnacle, he appeared.