Sima You

Sima You (; 246 – 27 April 283), courtesy name Dayou , posthumously known as Prince Xian of Qi , was an imperial prince of the Western Jin dynasty of China. He was the second son of Sima Zhao, a regent of the Cao Wei state during the Three Kingdoms period, and Zhao's wife Wang Yuanji. His wife was a daughter of Jia Chong and Jia's first wife Li Wan; Li Wan herself was a daughter of Li Feng.

Sima You accompanied his grandfather Sima Yi as he put down Wang Ling's rebellion. He also became the heir to his uncle, Sima Shi, who eventually died in March 255 without any sons. It is known that Sima You was a person of mild-mannered character, who was expected to become King of Jin, but ended up being passed over due to his young age. The heir that was eventually chosen was Sima Zhao's first son, Sima Yan (Emperor Wu), who usurped the Cao Wei throne and established the Jin dynasty with himself as the new emperor in February 266. Sima You was made Prince of Qi on 9 February 266. Empress Dowager Wang worried about Emperor Wu acting against Sima You; on her deathbed in April 268, while in tears, she told Emperor Wu, "Taofu is rash, while you are not benevolent as an elder brother. After my death, you two are unlikely to tolerate each other. Thus, I entrust him to you. Please don't forget my words."

After Emperor Wu appointed his developmentally disabled eldest son Sima Zhong heir apparent, he was concerned that his subjects viewed Sima You too favourably. One such incident occurred between August 272 and 274, while Xiahou He was still Intendant of Henan. Emperor Wu had become gravely ill, and the Jin court considered making Sima You the next emperor, rather than Sima Zhong. Xiahou told Jia Chong, "Your relations with both sons-in-law are equal. An heir should be chosen based on his virtues." Jia did not comment on the statement; after Emperor Wu heard about the incident, he moved Xiahou to the post of Minister of the Household, and deprived Jia of his military command, while allowing Jia to retain his titles and treatment in court. Despite this, Emperor Wu continued to bestow titles upon Sima You, including the post of sikong on 16 September 276, replacing Jia Chong (who was made Grand Commandant).

In order to strengthen Sima Zhong's position, he ordered Sima You away from Luoyang in January 283 to his fiefdom of Qi, despite protestations from their sisters, Princess Jingzhao and Princess Changshan. With his father-in-law Jia Chong having died a few months earlier in May 282, Sima You had one fewer powerful voice to intercede on his behalf. Sima You fell ill from the stress and died soon after in April 283 at the age of 38 (by East Asian age reckoning). Emperor Wu decreed that the funeral rites for You's funeral follow those of their great-uncle, Sima Fu.

Sima You's son, Sima Jiong, was one of the eight princes involved in the War of the Eight Princes during the reign of Emperor Hui, the second emperor of the Jin dynasty.