Emperor Ruizong of Tang (b. 662)
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 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 domineering 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 puppet under control of his mother and had no real power. From then onwards, the Tang Dynasty existed only in name and Empress Dowager Wu ruled China for over six years as acting 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.

In 705, a coup overthrew Wu Zetian and restored Emperor Zhongzong to the throne. The five years of Emperor Zhongzong's reign were dominated by Zhongzong's empress consort, Empress Wei. In the beginning of July 710, Emperor Zhongzong died, allegedly poisoned by Empress Wei who then named Zhongzong's youngest son Li Chongmao the Prince of Wen emperor (as Emperor Shang). A mere two weeks later, Li Dan's sister Princess Taiping and Li Dan's son Li Longji the Prince of Linzi launched a coup which resulted in the death of Empress Wei. Princess Taiping, Li Longji, and Li Longji's brother Li Chengqi the Prince of Song then persuaded Li Dan to take the throne himself, and he agreed, returning to the throne in Emperor Shang's stead. Li Longji, although not the oldest son, was made crown prince on account of his accomplishments.

Soon, however, tensions between Princess Taiping, who had exceedingly power, complete trust of the emperor and many supporters, and Li Longji (who was created crown prince) mounted. Li Longji constantly criticized his aunt for influencing his father's administration, which was in vain, instead Princess Taiping also responded to the proposal to remove him from the post of crown prince, which was in vain. Eventually, in September 712, Emperor Ruizong, believing that astrological signs called for a change of emperors, abdicated in favor of Li Longji (as Emperor Xuanzong). However, at Princess Taiping's suggestion, Emperor Ruizong, now carrying the title of Taishang Huang (retired emperor), continued to wield actual and superior power. This allowed Princess Typing to continue to participate and influence in governmental affairs without change and still had the power to stubbornly resist and bitter fight against Li Longji (now Emperor Xuanzong). Eventually, in 713, suspecting Princess Taiping of planning a coup, Emperor Xuanzong acted first, killing her associates and forcing her to commit suicide. After the death of Princess Taiping, Emperor Ruizong himself yielded imperial powers to Emperor Xuanzong and left the governmental scene. He died in 716.