Emperor Ruizong of Tang, 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 (684–690), when he was controlled by his mother. During his second reign after his mother's death, significant power and influence was exercised by his sister Princess Taiping.