The Creator refused the post so her parents were made the leader of the gods. The reason for it was that one of them was in charge of the law of Life, while the other handled the laws of Death, two of the most powerful laws.
During their reign, many rules were created, like one could no longer go back and forth the two realms anymore. And that to gain followers, a god could not manifest by himself, only create miracles or aid the believer in magic.
One way or another, the world became a bit chaotic and religions kept clashing against each other. Gods competed for supremacy and faiths. Yet the situation gradually became the norm as the gods and humans both became accustomed to it.
This persisted until all of a sudden... the Creator went mad.