Sima Yan (司马炎) was the founder and first emperor of the Jin Dynasty in ancient China. He reigned from 265 to 290 AD.

Sima Yan was a member of the Sima family, a prominent aristocratic family in the Wei state during the Three Kingdoms period. He was the son of Sima Zhao, the regent of the Wei state, and succeeded his father as the ruler of the state.

In 265 AD, Sima Yan deposed the last emperor of the Wei state, Cao Huan, and established the Jin Dynasty. He took the title of Emperor Wu of Jin and established his capital in Luoyang.

During his reign, Sima Yan oversaw the reunification of China, conquering the kingdoms of Shu and Wu, which had been established during the Three Kingdoms period. He also implemented various policies to promote economic development, education, and culture.

However, Sima Yan's reign was also marked by corruption, nepotism, and internal conflicts. He was known for his extravagance and his reliance on eunuchs, which weakened the imperial court.

Overall, Sima Yan played an important role in Chinese history, marking the beginning of the Jin Dynasty and the reunification of China after a period of division.