Empress regnant in the context of "Josei Tennō"

The Tang dynasty (/tɑːŋ/, [tʰǎŋ]; Chinese: 唐朝), or the Tang Empire, was an imperial dynasty of China that ruled from 618 to 907, with an interregnum between 690 and 705. It was preceded by the Sui dynasty and followed by the Five Dynasties and Ten Kingdoms period. Historians generally regard the Tang as a high point in Chinese civilisation, and a golden age of cosmopolitan culture. Tang territory, acquired through the military campaigns of its early rulers, rivalled that of the Han dynasty.

The Li family founded the dynasty after taking advantage of a period of Sui decline and precipitating their final collapse, in turn inaugurating a period of progress and stability in the first half of the dynasty's rule. The dynasty was formally interrupted during 690–705 when Empress Wu Zetian seized the throne, proclaiming the Wu Zhou dynasty and becoming the only legitimate Chinese empress regnant. The An Lushan rebellion (755–763) led to devastation and the decline of central authority during the latter half of the dynasty.

An emperor (from Latin: imperator, via Old French: empereor) is the (male) ruler of an empire. Empress, the female equivalent, may indicate an emperor's wife (empress consort), mother/grandmother (empress dowager/grand empress dowager), or a woman who rules in her own right and name (empress regnant or suo jure). Emperors are generally recognized to be of the highest monarchic honour and rank, surpassing king. In Europe, the title of Emperor has been used since the Middle Ages, considered in those times equal or almost equal in dignity to that of Pope due to the latter's position as visible head of the Church and spiritual leader of the Catholic part of Western Europe. The emperor of Japan is the only currently reigning monarch whose title is translated into English as "Emperor", although he no longer reigns over an empire.

Both emperors and kings are monarchs or sovereigns, both emperor and empress are considered monarchical titles. In as much as there is a strict definition of emperor, it is that an emperor has no relations implying the superiority of any other ruler and typically rules over more than one nation. Therefore, a king might be obliged to pay tribute to another ruler, or be restrained in his actions in some unequal fashion, but an emperor should in theory be completely free of such restraints. However, monarchs heading empires have not always used the title in all contexts—the British sovereign did not assume the title Empress of the British Empire even during the incorporation of India, though she was declared Empress of India.

Empress Zetian (624 – 16 December 705), commonly known as Wu Zetian, personal name Wu Zhao, was the empress regnant (huangdi, 皇帝) and only ruler of the (Wu) Zhou dynasty from 690 to 705. She had previously held power as the second wife and empress consort of Emperor Gaozong of the Tang dynasty from 660 to 683 and as empress dowager during the reigns of her sons Emperors Zhongzong and Ruizong of Tang between 683 and 690, holding de facto power during these periods. She was the only female sovereign in the history of China who is widely regarded as legitimate. Modern scholarship has re-examined Wu Zetian's rule beyond traditional portrayals of manipulation and cruelty. Recent studies highlight her administrative reforms, expansions of the civil-service examination system, and support of Buddhist symbolism as instruments of governance and legitimacy. During her 45 year tenure, China grew larger, its culture and economy were revitalized, and corruption in the court was reduced. She was eventually removed from power during the Shenlong Coup [zh] and died a few months later.

In early life, Empress Wu was a concubine of Emperor Taizong. After his death, she married his ninth son and successor, Emperor Gaozong, officially becoming Gaozong's empress, the highest-ranking of his consorts, in 655. Empress Wu held considerable political power even before becoming empress, and began to control the court after her appointment. After Gaozong's debilitating stroke in 660, she became administrator of the court, a position with similar authority to the emperor's, until 683. History records that she "was at the helm of the country for long years, her power no different from that of the emperor". On Emperor Gaozong's death in 683, rather than entering retirement, and not interfering in the government, Empress Wu broke with tradition and took acquisition of complete power, refusing to allow either of her sons to rule. She took the throne in 690 by officially changing the name of the dynasty from Tang to Zhou, changing the name of the imperial family from Li to Wu, and holding a formal ceremony to crown herself as emperor.

Emperor Gaozong of Tang (21 July 628 – 27 December 683), personal name Li Zhi, was the third emperor of the Chinese Tang dynasty, ruling from 649 to 683; after January 665, he handed power over the empire to his second wife Empress Wu (the future Wu Zetian), and her decrees were carried out with greater force than the decrees of Emperor Gaozong's. Emperor Gaozong was the youngest son of Emperor Taizong and Empress Zhangsun; his elder brothers were Li Chengqian and Li Tai.

Emperor Gaozong's reign saw the primacy of Empress Wu, who became the effective power behind the Tang rule. Empress Wu aided Emperor Gaozong in his rule during the later years of his reign after a series of strokes left him incapacitated. Emperor Gaozong effectively after January 665 delegated all matters of state to Empress Wu; after that the empress acted as the power behind the emperor, "hanging the curtain and listening to politics" (垂簾聼政; Chuílián tīngzhèng). Gaozong's personal illness, affection and trust of Wu led to her wielding a great deal of power in affairs of state until the end of his reign. From official histories from the later Tang Dynasty to contemporary historians, there exists a lively debate about whether Wu exerted undue influence on Gaozong, or whether they were equal partners in the government. Empress Wu was partially in control of power from November 660 and then totally from January 665 to December 683; there was an equality of power between Gaozong and Wu, which caused them to be called "two saints" (二聖; Er Sheng, literally two emperors) both inside and outside. After Emperor Gaozong died in December 683, power fell completely and solely into the hands of Empress Wu, acting as Empress Dowager-regent, "presiding over court and issuing edicts" (臨朝稱制; lin chao chengzhi); she subsequently became the only empress regnant in Chinese history. After his death, he was interred at the Qian Mausoleum along with Wu Zetian.

The Trưng sisters, known in Vietnamese as Hai Bà Trưng (Vietnamese pronunciation: [haj ɓa t͡ɕɯŋ], 𠄩婆徵, "Two Ladies [named] Trưng") or simply Hai Bà ("The Two Ladies"), c.14 – c. 43) were Lac Viet military leaders who ruled for three years after commanding a rebellion of Lac Viet tribes and other tribes in AD 40 against the first Chinese domination of Vietnam. They are regarded as national heroines of Vietnam. Their names were Trưng Trắc and Trưng Nhị. Trưng Trắc was the first female monarch in Vietnam, as well as the first queen in the history of Vietnam (Lý Chiêu Hoàng was the last woman to take the reign and is the only empress regnant), and she was accorded the title Queen Trưng in the Đại Việt sử ký toàn thư.

The sisters were born in Jiaozhi (Giao Chỉ), a commandery of the Chinese Han dynasty in modern-day northern Vietnam. The dates of their births are unknown, but Trưng Trắc was older than Trưng Nhị. The exact dates of their deaths are also unknown but both died around 43 AD after battling against the punitive expedition force led by Eastern Han general Ma Yuan.