Well, as you have phrased your question, I would suggest that it depends on how one defines what a god is. If you accept that a god is a powerful ruler, then I would suggest there would be many gods, and there would be no grounds to claim that there is only one god. But there can only be one God.
The definition itself of what "God" is repudiates the possibility for there being more than one.
God is defined as: the creator and ruler of the universe and source of all moral authority; the supreme being.
(
https://www.google.com/#q=God+def)
God is "
the sole Supreme Being, eternal, spiritual, and transcendent, who is the Creator and ruler of all and is infinite in all attributes."
(
http://www.thefreedictionary.com/god)
God is "the creator and ruler of the universe; Supreme Being."
http://www.thefreedictionary.com/god
There can only be on "Supreme Being". If it could be imagined that there could be two Supreme beings, we could simply ask ourselves which one is more supreme. How could one being differ from another and yet remain equally supreme to the other? It can't happen. If they are equally supreme, we have somewhat of a conundrum. If they are equally supreme, and equal rulers of the universe, and play equal roles in creation, how would we distinguish one from the other? We couldn't. The two would by necessity have to be one.
These definitions do not suggest that God is "a" creator, but "the" one and only creator of the universe. Anyone can be a god, but there can be only one God.