Cheng of Jin, emperor of the Jin Dynasty (born 321)

Emperor Cheng of Jin, personal name Sima Yan (司馬衍), courtesy name Shigen (世根), was an emperor of the Chinese Eastern Jin dynasty. He was the eldest son of Emperor Ming and became the crown prince on April 1, 325. During his reign, the administration was largely dominated by a succession of regents—initially his uncle Yu Liang, then Wang Dao, then the joint administration of He Chong and another uncle Yu Bing. He became emperor at age four, and soon after his accession to the throne, the disastrous rebellion of Su Jun weakened Jin forces for decades.