The Prologue establishes a bit of background about Gilgamesh, giving us an insight into what kind of man he is. The narrator tells us that he will recount the great deeds of Gilgamesh, indicating at once just what kind of man we're dealing with here. And yet, as the narrator goes on to tell us, Gilgamesh is no mere ordinary mortal; he's two-thirds god and one-third man. Once again we're being prepared for what's about to follow, of the extraordinary feats that Gilgamesh will accomplish in his epic quest to reconcile himself with death.
The Prologue leaves us in no doubt as to Gilgamesh's heroic status; it also highlights the fact that what's about to follow is a transcription by the narrator of Gilgamesh's own story, a story he himself wrote down on tablets of clay. By drawing our attention to the telling of a tale, the narrator blurs the distinction between Gilgamesh's world and our own, placing us right at the heart of a story whose truth we might not readily accept.