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Yu Wenjun (Chinese: ; 297-328), formally Empress Mingmu (?, literally "the understanding and solemn empress") was an empress of the Chinese Jin dynasty (265-420) by marriage to Emperor Ming of Jin, and Regent during the minority of her son Emperor Cheng from 326 to 327.
Empress Yu's father Yu Chen () was the governor of Kuaiji Commandery along the southern shore of Hangzhou Bay and later served on the staff of Sima Rui the Prince of Langye (later Emperor Yuan) when Sima Rui was posted at Jianye. She was considered kind and beautiful, and Sima Rui took her to be his son Sima Shao's wife. Her brother Yu Liang became a key friend and advisor to Sima Shao. Later, after Sima Rui declared himself emperor and created Sima Shao crown prince, she became crown princess. After Emperor Yuan died in 323 and Sima Shao succeeded to the throne as Emperor Ming, she became empress. She bore him two sons, Sima Yan and Sima Yue).
Emperor Ming only ruled briefly and died in 326. Initially, he left a balance of power between high-level officials with whom he entrusted the four-year-old Crown Prince Yan, who later succeeded to the throne as Emperor Cheng. Empress Yu was honored as Empress Dowager Yu, and the officials encouraged her to become regent. Under this arrangement, Yu Liang became the most powerful official of the empire. He became apprehensive of the generals Su Jun, Zu Yue (), and Tao Kan, each of whom suspected Yu of erasing their names from Sima Shao's will, which promoted and honored a large number of officials. Yu Liang was also apprehensive of Emperor Ming's step-uncle Yu Yin () and the Imperial Princes Sima Zong () the Prince of Nandun and Sima Yang () the Prince of Xiyang, all of whom were powerful during Emperor Ming's reign but who had been removed under Empress Dowager Yu's regency. In winter 326, Yu Liang accused Sima Zong of treason and killed him, demoted Sima Yang, and exiled Yu Yin. This led to the people losing confidence in him.
In 327, Yu Liang further resolved on separating Su, then the governor of Liyang Commandery (, roughly modern Chaohu, Anhui) from his troops, and he promoted Su to minister of agriculture--a post that did not involve commanding troops. Su saw his intent and declared a rebellion, with Zu's assistance. Yu Liang initially thought that Su could be easily defeated, but instead Su quickly arrived at the capital early 328 and captured it. Yu Liang was forced to flee. Meanwhile, Su pillaged the capital, and it was said that even Empress Dowager Yu's servant girls became spoils for his troops. Further, it was said that Su himself "humiliated" Empress Dowager Yu -- although the method of humiliation was not specified in history. She died in distress and fear. Her son Emperor Cheng would become Su's captive for months before other provincial generals would converge on Jiankang and defeat Su.