Earliest historical Chinese monarch

Feb 2019
List of Chinese monarchs - Wikipedia

According to tradition, it is either Youchao, Yellow Emperor or Yu the Great, but afaik historians regard these as mythical figures. Qin Shi Huang is sometimes known as first emperor of a unified China, and the Bamboo Annals were written during the reign of King Xiang of Wei. How far back can we go and call a Chinese Emperor a generally regarded historical figure, and not just semi-legendary?