Wu Sansi in the context of Shangguan Wan'er

Emperor Ruizong of Tang (22 June 662 – 13 July 716), personal name Li Dan, also known at times during his life as Li Xulun, Li Lun, Wu Lun, and Wu Dan, was the fifth and ninth emperor of the Chinese Tang dynasty. He was the eighth son of Emperor Gaozong and the fourth son of Emperor Gaozong's second wife Empress Wu. He was wholly a figurehead during his first reign when he was controlled by his mother, and he was the titular and puppet ruler of the Tang Empire from 684 to 690. During his second reign after his mother's death, significant power and influence was exercised by his sister Princess Taiping.

In February 684, Li Dan's mother Empress Wu demoted his older brother Emperor Zhongzong (Li Xian) who had attempted to rule free of his mother and named him emperor (as Emperor Ruizong). Emperor Ruizong, however, was a hollow figurehead under control of his mother and had no real power, even nominally, his name was not included in the issued documents or orders. He was not even able to move freely around his private residence, let alone attend to governmental affairs. From then onwards, the Tang dynasty existed only in name and Empress Dowager Wu ruled China for over six years as quasi-emperor. Empress Wu, was comfortable about the empire being entirely under her control, decided finally to seize the throne, so in October 690 Emperor Ruizong ceded the imperial throne to his mother, who installed herself as empress regnant – the only woman in Chinese history ever to rule with this title. She issued a decree that ended the Tang dynasty and founded the Zhou dynasty. Emperor Ruizong was reduced to the position of crown prince, with the unconventional title of Huangsi (皇嗣, "imperial successor"). In the following years, Empress Wu's nephews Wu Chengsi and Wu Sansi tried to have one of them named heir to the throne, but Wu Zetian resisted these calls. Eventually, in October 698, faced with foreign invasion and dissatisfaction at home, Empress Wu accepted the suggestion of the chancellor Di Renjie and recalled the exiled Li Xian to the capital Luoyang. Soon, Li Dan offered to yield the position of crown prince to his elder brother, and Li Xian became crown prince instead.