I. The Angels
Humans. Humans beings were not the first, nor the last intelligent life forms created by God. There are many different opinions and accounts as to who or what exactly were the very first life forms to be created by God. But, the only closest thing that we have to a record of what or who came before human beings is recorded in most of our religious works such as ancient Jewish scrolls and mesopotamian and Persian tablets. According to each different culture and religion, they are called many different names. Some, like the ancient mesopotamians, called them the Annunaki, while the Persians called them the Ahuras. But, I like to call them by the name the religion of my early upbringing called them: Angels.
Those are at least one kind of intelligent being that pre-existed and pre-dated humans. And, they had a lot to do with the early days of humanity, once co-existing alongside human beings, sometimes taking on a human or humanoid form and mortal mothers sometimes bore their children, most appearing pretty normal, but sometimes others would grow into giants. These are where we got our ancient tales of giants from ancient Greek and European mythologies. But, the Hebrews called them the Nephilim.
These were half breeds from a s****l union between Mortal humans and angels. So, when the great war broke out between Mortal human beings and their kind, some of the half breeds sided with humanity, while some sided with the angels. Not many really know exactly what caused the war or who started it. But, this much is clear. Even the angels themselves were divided. Divided according to allegiance either to the creator, or to other powerful angels that wished either to conquer heaven or to play by their own rules. Many say they left and flooded the earth in order to destroy most of humanity in order to teach them a lesson never to repeat their treachery ever again. But, some say that some of the Nephilim half breeds survived the flood and that angelic half breeds still walk amongst us in secret, or that even the Archangel Michael occasionally visits our "dark and fallen world" to ensure humanity's allegiance to them and the creator. But, the "demons", a.k.a the fallen also want humanity's allegiance. Most people think they want to use human beings as part of their army, because Earth is actually contested territory between two or more clans of angels. But, we will have to go even further back in time in order to truly understand the truth: how the great rift between the angelic clans started in the first place....
We will have to go all the way back to before the first rebellion. The rebellion of the fallen against the Archangels and God.