Emperor Ruizong of Tang was the eighth son of Emperor Gaozong and the fourth son of Emperor Gaozong's second wife Empress Wu (later known as Wu Zetian). 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 did not have any real power.

In October 690 he ceded the imperial throne to his mother; who installed herself as Empress regnant - the only woman in Chinese history ever to rule as emperor. 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 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 many supporters; and Li Longji mounted. 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 power. However; 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.