According to the Sumerian King List, Gilgamesh is said to have ruled Uruk for 126 years.
The Sumerian King List is a Mesopotamian historiographical text that presents kings and the lengths of their reigns, often combining historical rulers with legendary figures. Gilgamesh appears among the kings of Uruk, and the list assigns him an extraordinarily long reign.
The figure is not treated by historians as a reliable modern-style chronology. The list uses very large reign lengths for several early rulers, reflecting the legendary character of its earliest sections. Gilgamesh may nevertheless have been based on a real ruler who lived in the early part of the third millennium BCE.
The 126-year figure belongs to the king-list tradition, not to the narrative events of the Epic of Gilgamesh. The epic itself focuses on kingship, friendship, grief and the search for lasting fame rather than giving a precise historical biography.