Emperor Ruizong of Tang no relation Emperor of China
During the reign of Emperor Gaozu of Tang (618-626):
Lady Wu (from 624)
During the reign of Emperor Taizong of Tang (626-649):
Talented Lady (才人; from 637), 17th rank consort
During the reign of Emperor Gaozong of Tang (649-683):
Imperial Concubine Zhaoyi (昭儀; from 650), 6th rank consort
Empress (皇后; from 655), 1st rank consort   
Heavenly Empress (天后; from 674), 1st rank consort
During the reign of Emperor Zhongzong of Tang (684-684):
Empress Dowager Wu (武皇太后; from 683)
During the reign of Emperor Ruizong of Tang (684-690)
Empress Dowager Wu (武皇太后; from 684)
During her reign as the Empress Regnant of the Zhou Dynasty (690-705):
Holy Emperor (聖神皇帝; from 690)
Holy Golden Emperor (金輪聖神皇帝; from 693)
Holy Golden Goddess Emperor (越古金輪聖神皇帝; from 694)
Holy Golden Emperor (金輪聖神皇帝; from 695)
Emperor Tiance Jinlun (天策金輪大帝; from 695)
Emperor Zetian Dasheng (則天大聖皇帝; from 705)
During the second reign of Emperor Zhongzong of Tang (705-710):
Empress Zetian Dasheng (則天大聖皇后; from 705)
During the second reign of Emperor Ruizong of Tang (710-712):   
Heavenly Empress (天后; from 710)    
Holy Empress (大聖天后; from 710)   
Empress of Heaven (天后聖帝; from 712)
Holy Empress (聖后; from 712)
During the reign of Emperor Xuanzong of Tang (713-756):   
Empress Zetian (則天皇后; from 716)
Holy Empress Zetianshun (則天順聖皇后; from 749)"Empress"
Various Chinese titles have been translated into English as "empress", including "empress" in both the sense of empress consort and empress regnant. Generally, the monarch was male and his chief spouse was given a title such as huanghou (皇后), often translated as "empress" or more specific "empress consort". Upon the emperor's death, the surviving empress consort could become empress dowager, sometimes wielding considerable political power as regent during the minority of the (male) heir to the position of emperor.
Since the time of Qin Shi Huang (259–210 BC), the Emperor of China using the title huangdi (皇帝, translated as "emperor" or "empress (regnant)" as appropriate), Wu was the only woman in the history of China to assume the title huangdi. Her tenure as de facto ruler of China and official regent of the Tang dynasty (first through her husband and then through her sons, from 665 to 690) was not without precedent in Chinese history, but she broke precedent when she founded her own dynasty in 690, the Zhou (周) (interrupting the Tang dynasty), ruling personally under the name Sacred and Divine Huangdi (聖神皇帝), and variations thereof, from 690 to 705.
Wu Zetian and Empress Dowager Liu of the Song Dynasty are said to be the only women in Chinese history to have worn a yellow robe, ordinarily reserved for the emperor's sole use, as a monarch or co-ruler in their own right.Modified Chinese characters
In 690, Wu's cousin's son Zong Qinke submitted a number of modified Chinese characters intended to showcase Wu's greatness. She adopted them, and took one of the modified characters, Zhao (曌), to be her formal name (i.e., the name by which the people would exercise naming taboo on). 曌 was made from two other characters: Ming (明) on top, meaning "light" or "clarity", and Kong (空) on the bottom, meaning "sky". The implication appeared to be that she would be like the light shining from the sky. (Zhao (照), meaning "shine", from which 曌 was derived, might have been her original name, but evidence of that is inconclusive.) Later that year, after successive petition drives started by the low-level official Fu Youyi began to occur in waves, asking her to take the throne, Emperor Ruizong offered to take the name of Wu as well. On 18 August 690, she approved the requests. She changed the state's name to Zhou, claiming ancestry from the Zhou dynasty, and took the throne as Empress Regnant (with the title Empress Regnant Shengshen (聖神皇帝), literally "Divine and Sacred Emperor or Empress Regnant"). Ruizong was deposed and made crown prince with the atypical title Huangsi (皇嗣). This thus interrupted the Tang dynasty, and Wu became the first (and only) woman to reign over China as empress regnant.
no relation