The original Chief God is a divinity and the attributed creator of the Monster Girl Encyclopedia world. The Order maintains that the current Chief God is eternal and all-powerful, and therefore that the present head deity is the original head deity. However, in describing the Demon Lord's rise to power, the Wandering Scholar reports that, "just as in the case of the demon lord, a new chief god took over, but she was a goddess who was still very inexperienced."
Nowhere are details given on how frequently the title of "chief god" changes hands, what causes it to change hands, or where former chief gods go. Regardless of the identity of the original Chief God, both Order and monsters agree that they were responsible for the creation of the world and for writing the metaphysical "rules" which the current Demon Lord is fighting against. Where the two accounts differ is on the origin of monsters: Order sources state that the monsters "emerged from the darkness" contrary to the Chief God's plan, while the Demon Lord maintains that monsters were part of the world from its inception.
It is the omnipotent and omniscient creator god who gave birth to humans and subdued many of the other gods. [...]
Monster Girl Encyclopedia I, "The Truth"
[...] First off, it's true that the [original] chief god created the world and humans. But the demon lord and the monsters were included as part of the “world” that the chief god created. Saying that the demon lord is a being who emerged from the darkness is a huge lie on the part of the gods and The Order. [...] They're living creatures the chief god created so that it could adjust the number of humans. The demon lord who The Order insists is wicked, was created as a control device so that the gods could control the monsters. [...]
[...] One was that she happened to be a succubus, a being that builds up power by having sex with men; one was that her current husband, who was the hero at the time, sympathized with her ambition and cooperated with her; one was that the monsters lent her their strength for some reason even though up to that point they had always fought endlessly amongst themselves, killing even their own kind in the struggle to decide a demon lord; and one was that just as in the case of the demon lord, a new chief god took over, but she was a goddess who was still very inexperienced. [...]