Sima Yi (179 – September 7, 251) is a general and politician of the state of Cao Wei during the Three Kingdoms era of Chinese history.

He is perhaps best known for defending Wei from Zhuge Liang's Northern Expeditions.

His success and subsequent rise in prominence pave the way for his grandson Sima Yan's founding of the Jin Dynasty, which will eventually bring an end to the Three Kingdoms era.

In 265, after the Jin Dynasty is established, Sima Yi is posthumously honored as Emperor Xuan of Jin with the temple name of Gaozu.