The Five Emperors, or Wu Di in Chinese, were the five mythical rulers of ancient China who succeeded the Three Augusts prior to the beginning of the dynasty system of government. Their existence is reflected only in traditional histories and legend - there is not archaeological evidence for them, and the categorization of these rulers is questionable, as some sources omit certain rulers or designate them differently.
The Wu Di were legendary as the five perfect earthly emperors - not the offspring of Gods as were the Three Augusts but men of infinite wisdom. Their rule was from approximately 2700-2200 BCE. The dates below are of course questionable, drawn from histories whose own dates cannot be precisely determined. Generally, the Five Emperors designate the following.
Ruled 2697-2597 BCE. He is the ancestor of all of the Han people, and the sponsor of learning whose scholars created Chinese characters, measurements, the calendar, and music. He wrote the Huang Di Nei Jing, the book of medicine that forms the basis of Chinese medicine today. He united China under one ruler, ending the tribal period that the Three Augusts had ruled over.
Zhuanxu (or Gaoyang)
Ruled 2513-2435 BCE. The grandson of Huangdi, Zhuanxu helped hasten the assimilation of the neighboring tribes by banning their Shamanistic customs and instead imposing Han morals and relgion upon them.
Ku (or Gaoxin)
Ruled 2435-2365 BCE. Ku was the nephew of Zhuanxu (this was a normal pattern of succession in the age) and therefore great-grandson of the legendary Huangdi. Both Ku and Zhuanzhu appear little in legend.
Yao (or Tangyao)
Ruled 2357-2255 BCE. Yao was most reknowned for his compassion and justice in the administration of China. He was originally a duke and ascended to the throne as a replacement for Zhi, the son of Ku. Yao invented the game of Go to amuse his son, Danzhu; it came to him in a dream in which Huangdi played it in preparation for battle. He chose not to appoint is son to the throne, because Danzhu had no interest except Go, appointing Shun instead.
Shun (or Yu)
Ruled 2255-2205 BCE. Shun was the legendary founder of the dynasty system. He was a commoner, the son of a blind man and part of a family of criminals. Shun thus sought to restore his family's honor and was appointed to rule under Yao over some of China. He was well liked and the people called for him to be appointed to the throne when Yao stepped down. Legend states that Shun used magic (or engineering) to rid China of flooding by leading nine rivers to the sea, saving the nation.
Note that although Shun was also known as "Yu", his successor, Emperor Yu, was not related. Yu founded the Xia Dynasty and some legends refer to him as one of the Wu Di.