Humans created god by attributing many of their own qualities unto an imaginary 'being'. But they also gave him a bit more than what they themselves were: they made him all-powerful and all-knowing! So are the fictional places that human beings created in their grand fantasies called Paradise, Hell and the Kingdom of God! But they did not create one god; they created hundreds and thousands of gods and goddesses in many old cultures and societies.
But in the early history of humankind, the forces of nature, like thunder, storms, rain, etc., overawed humans. They were not able to explain these powerful and frightening forces of nature that affected them. As a result, they started to do whatever they could to placate them by making occasional sacrifices to them and entreating them for mercy and kindness.
The idea of deities came much later when they developed anthropomorphic ideas relating to deities they came to believe in that were distinct from the earlier worship of the forces of nature.
Since then, the story of gods in various forms and shapes had become a dominant factor in their lives. The movement from the plurality of deities to smaller numbers was gradual. In some cultures, there was further reduction in such numbers, coming down to three, two or only one. They are all part of the history of the evolution of the notions of powerful supernatural or divine beings.