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From what I barely know about Gilgamesh from popular media is that he was a Hero of Mesopotamia, their first King? Maybe? And he also created civilization? I think? I should probably look it up on google. But he was a very arrogant hero that unified the ancient tribes of people together to create the great kingdom or something.
Also he was the protagonist of the Epic of Gilgamesh, perhaps one of the first heroic epic stories in history, maybe. And where most of fictional literature regarding heroes comes from, slowly changing over the years, but that's always follows these certain tropes.
It is a millenary tale and story, and I think he might have been a historical king of Uru… Uruk? But he was somehow deified, kind of like what sometimes happens with Pharaohs where they die and turn into new Egyptian Gods added into the pantheon later.