meaning of Gilgamesh reference

Gilgamesh was a possibly mythical but probably historical Sumerian king who ruled the city of Uruk in Mesopotamia (now Iraq) around 2700 BC. He was considered a great king and a great hero for building an impregnable wall around the city to protect its people from enemy invasion.

In this context, he may be considered the ultimate hero in Gwen and David's pantheon of heroes, along with Batman (but not Superman), the one man who would be able to give David the heroic passion, support and security he's searching for. But since Gilgamesh is either a myth or dead nearly 5000 years, he's also completely unavailable, so David may also be saying he's looking for a hero he knows he'll never find.

I'm just guessing. Only the writer of the screenplay knows for sure what he meant.