Darwin Loves You
The idea that the Old Gods were anthropomorphic extraterrestrials is not too far fetched. There are numerous hieroglyphics that depict rocketship-like vehicles and talks of "celestial chariots" (flying objects that operate through space) as forms of transportation for the Gods.
Exactly how they came into existence is unclear, but it was most likely due to evolution. I believe that no matter how complicated or difficult to grasp it may be, science, reason, and logic can explain everything.
When you ask the question of who created them and answer "Almighty God and there is only one," then you would have to admitt that there are indeed other Gods (plural) which contradicts the whole concept of monotheism. When answering with "Almighty God and there is only one" to the question of who created the other Gods is a contraditicting statement itself. If you believe there is only one God then how could there be others. If he is "omnipotent" then how can anything exist without his allowence of it? If he is "all knowing" then why would he allow the existence of an opposition party, knowing that it will "deceive" so many of his "lost souls," denying them his "truth"?
Darwin Loves You.