Sima You

Sima You (248–283), courtesy name Dayou, was an imperial prince of the Jin dynasty (265–420) of China. He was the second son of Sima Zhao, a regent of the Cao Wei state during the Three Kingdoms period. Sima You became the heir to his uncle, Sima Shi, who at the time was sonless. It is known that Sima You was a person of mild-mannered character who was expected to be appointed emperor, but ended being passed over due to that of his young age. The heir that was 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 265.

When Emperor Wu appointed his developmentally disabled son heir apparent, he was concerned that his subjects viewed Sima You too favourably. In order to strengthen his son's position, he ordered Sima You away from Luoyang in 282 to a vassal state, despite protestations from their sisters, Princess Jingzhao and Princess Changshan. Sima You fell ill from the stress and died soon after at the age of 36 (by East Asian age reckoning).

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.