Gilgamesh can be portrayed as a powerful and haughty figure. He could walk around the world of Danmachi with an air of superiority, looking down on the 'lesser' adventurers. His flamboyant style and his love for grandeur can be emphasized, like always wearing the most elaborate and expensive armor.
In the story, they start as sort of rivals. Gilgamesh is a powerful king who is a bit wild, and when Enkidu is created, he challenges Gilgamesh. But then they become friends. They share a deep bond that is tested through various trials. For example, when they face Humbaba, the demon of the cedar forest. Their relationship is complex and full of mutual respect in the end, and Enkidu's death deeply affects Gilgamesh.
The story of Gilgamesh is an ancient epic that follows the adventures and quests of the king Gilgamesh. It explores themes of friendship, mortality, and the search for meaning.
The Epic of Gilgamesh is not classified as a novel. It predates the concept of the novel and has different characteristics and structures. It's more like an epic poem or mythological tale.
He could be integrated as a powerful enemy at first. He might target the academies because he sees them as places that are trying to control and limit power, which goes against his own philosophy. However, as the story progresses, he could have a change of heart after seeing the selfless acts of the RWBY characters. He could then use his powers to help them against a common enemy like Salem.
There were a few novels that fit this description, such as Legend of the Earth Emperor, Mountain God in the City, Incense Becomes God, I Actually Became a Mountain God, and so on. You can choose one according to the plot introduction of these novels and your own taste. I wish you a happy reading!