Empresses
Empresses usually acquired their power after the death of their Emperor husband. After an emperor died, empresses would get the title of Dowager Empress. As a Dowager Empress, these women would sometimes act as regent.
Lu of Han
I was the wife of Hui-ti, who died in 188 B.C. I had no children of my own, so the child of one of Hui-ti's consorts was made emperor. His name was Shao-ti Kung. After 3 years, he was replaced by another child who was still an infant, named Shao-ti Hung. Because of the child emperors, I was able to act as regent.
(Cambridge History, vol 1 1986: 135-136)
Wu Zetian of Tang
I was a concubine of Gaozong. I influenced him so much in the years from 650 C.E. and 683 C.E., that I replaced his first Empress. Gaozong suffered from a stroke in 660 C.E. and I took control of the Empire. Gaozong died in 683 C.E, but I maintened power through my two sons.
I deposed both of my sons and proclaimed myself Emperor of a new dynasty. This new dynasty was known as Zhou. I was the only woman in Chinese history to proclaim the title of "Emperor."
(Ebrey 2010: 116-117)
Cixi of Qing
In the late 19th century there was a move for reform in China. This is not something I approved of.
In 1898 I made the mistake of allowing my 23 year old nephew, Guangxu, to rule. Guangxu was interested in the ideas of reform. He called on Kang Youwei to help him with reform. Kang Youwei was a leader of a group urging for modernizing and presented Confucius as an “institutional innovator and proponent of change.” With the help of Kang Youwei, passed a number of edicts for reform. Some of these edicts dealt with education, government, and commerce. After three months, I had enough of the reform. I did not want the reform to interfere with my power. I locked Guangxu in prison and had as many of the reformers as I could killed. Unfortunately, Kang Youwei escaped to Japan.
(Ebrey 2010: )
References
Ebrey, Patricia Buckley. Cambridge Illustrated History of China. New York: Cambridge University Press, 2010. 2nd ed.
The Cambridge History of China, vol. 1. New York: Cambridge University Press,1986