Probably the oldest transmitted hero myth we know is from the period of the foundation of Babylonia (circa 2800 BC). It concerns the birth history of its founder, Sargon of Akkad.  He was best known for his conquests of the Sumerian city-states in the 24th to 23rd centuries BC. The Sumerian king list makes him the cup-bearer to king Ur- Zababa of Kish. Sargon appears as a legendary figure in Neo-Assyrian literature of the 8th to 7th centuries BC. Tablets with fragments of a Sargon Birth Legend were found in the Library of Ashurbanipal.

This episode is also available as a blog post: http://martinifisher.com/2018/12/07/sargon-karna-and-ion-hidden-sons-of-virgin-mothers/