The Epic of Gilgamesh doesn't have an official epigraph, but many scholars treat the first portion (the one that Kovacs entitles "The Legacy") as though it were an epigraph. This is a 27-line introduction to the story that essentially tells us why we should care about reading these twelve clay tablets.
The first few lines tells us that we will be reading about a man—so far unnamed—who has seen it all, experienced it all, known it all, and come back from a long journey to build the walls of Uruk. The remaining 18 lines discuss the beauty and strength of Uruk, and tell us that we can take from the walls a lapis lazuli (fancy blue stone) tablet that will tell us the details of this Gilgamesh's trials and tribulations.
So, no, it isn't officially an epigraph, but it does set the stage for the rest of the text. We know this Uruk place is a big deal, and we also know that Gilgamesh is totally the bomb. Since the next part of the epic begins telling us about what a jerk he is, we immediately realize that we are dealing with a dude that is going to develop into a good guy by the end of tablet 11.
Yeah, it kind of ruins the ending but, as you've probably noticed by now, the writer of Gilgamesh is not into using sophisticated literary techniques to keep you on the edge of your seat.