Huangdi (黃帝), “Emperor” or better Yellow Thearch, is a legendary culture hero of ancient China. In the Shiji he appears as Xuanyuan: he unifies clans, defeats Yan Di at Banquan and Chi You at Zhuolu, and reigns by Earth virtue — hence the yellow colour and the centre of the Five Phases.
He is not a modern-style historical emperor. Before Qin, “di” named a godly lord. Historians today read him as historicised myth: a god of the centre and of rain/earth who, in the Warring States and Han, became ancestor and patron of the state and the arts.
The Huangdi Neijing — Inner Canon of the Yellow Emperor — borrows that authority: Huangdi asks and his ministers answer. Thus the TCM classroom is born: yin–yang, Wu Xing, qi, channels. “Qi–Huang” (Qibo + Huangdi) became a metonym for Chinese medicine itself.