The Epic of Gilgamesh, despite many fictional or fantastical elements, is actually grounded in history. Gilgamesh appears as the king of Uruk in the Sumerian king lists. He was a real king and Uruk was a real city.
The first thing we learn is that Mesopotamian religion was polytheistic and anthropomorphic. There were many gods and goddesses, and they had the appearance and character of supernaturally powerful and immortal humans, albeit ones still bearing...