Sima Yi (; Chinese: 司馬懿; 179 CE – 7 September 251 CE), courtesy name Zhongda, was a Chinese military general, politician, and regent of the state of Cao Wei during the Three Kingdoms period of China.
He formally began his political career in 208 under the Han dynasty's Imperial Chancellor Cao Cao, and was quickly promoted to higher office. His success in handling domestic and military affairs such as governance and the promotion of agriculture, serving as an adviser, repelling incursions and invasions led by Shu and Wu forces, speedily defeating Meng Da's Xincheng Rebellion, and conquering the Gongsun-led Liaodong commandery, garnered him great prestige. He is perhaps best known for defending Wei from a series of invasions that were led by Wei's rival state Shu between 231 and 234.
In 239, along with another co-regent Cao Shuang, he was made to preside as a regent for the young Cao Fang after the death of latter's adoptive father, Cao Rui. Although amicable at first, the relationship soon deteriorated in light of Cao Shuang's corruption, extravagance, and attempts to curtail Sima Yi's political influence. In February 249, after carefully planning and building up support, Sima Yi ousted Cao Shuang from power in a coup d'état and had him and his associates executed.
Afterwards, Sima Yi became the primary authority in Wei, although in June 251 he faced some opposition from Wang Ling's rebellion, which he swiftly dealt with. Sima Yi died on 7 September 251, at the age of 71 or 72, and was succeeded by his eldest son Sima Shi.
For the remainder of Wei's history, state power was increasingly vested in the Sima clan, which led to the establishment of the Jin dynasty, which was founded by Sima Yi's grandson Sima Yan in February 266. After Sima Yan became emperor, he honoured his grandfather with the posthumous title Emperor Xuan of Jin and the temple name Gaozu. He was also the last common ancestor of all emperors of the Jin dynasty; while emperors of the Western Jin descended from Sima Zhao (his son with wife Zhang Chunhua), emperors of the Eastern Jin descended from Sima Zhou (his son with concubine Lady Fu).
Sima Yi's ancestral home was in Xiaojing (孝敬里), Wen County, Henei Commandery. His ancestor was Sima Ang the King of Yin (殷王), who briefly ruled one of the Eighteen Kingdoms during the transition period from the Qin dynasty to the Western Han dynasty before Liu Bang's general Han Xin conquered his territory, capturing Sima Ang and his capital city Zhaoge. In the early Han dynasty, Sima Ang's former kingdom, which was largely situated in Henei, became a commandery of the Han Empire and his descendants had lived there since.
Sima Jūn (司馬鈞), an eighth-generation descendant of Sima Ang and the great-great-grandfather of Sima Yi, served as a general of the Han Empire, holding the position General Who Conquers the West (征西將軍). Sima Jūn's son Sima Liang (司馬量) held the position Grand Administrator of Yuzhang, and Sima Liang's son Sima Jùn (司馬儁) served as Grand Administrator of Yingchuan. Sima Jùn's son Sima Fang served as the Prefect of Luoyang (洛陽令), Intendant of Jingzhao, and later as Cavalry Commandant (騎都尉) towards the end of the Eastern Han dynasty. Sima Yi was Sima Fang's second son.
Sima Yi had one elder brother Sima Lang (Boda) and six younger brothers. The eight Sima brothers were collectively known as the "Eight Das" because their courtesy names all ended with da (達).
Sima Yi displayed intelligence and great ambitions at a young age. He was knowledgeable and well-versed in Confucian classics. When chaos broke out in China towards the End of the Han dynasty, Sima Yi often expressed sympathy and concern for the people. Before he reached adulthood around the age of 19, Sima Yi once met Yang Jun, a commandery administrator who was known for spotting talents. Yang Jun described him as an "extraordinary talent". Cui Yan, a friend of Sima Yi's elder brother, Sima Lang, once said: "(Sima Yi) is intelligent, decisive, and unique. (Sima Lang) can't be compared to him."
Sima Yi and his family used to live in the imperial capital, Luoyang, where his father, Sima Fang, served as a government official. Sima Yi was raised in a strict Confucian manner: He was not allowed to visit his father unless summoned, to speak to his father without being explicitly addressed, and neither was he allowed to be seated in the same room as his father. In 190, when the warlord Dong Zhuo dominated the Han central government and wanted to relocate the imperial capital to Chang'an, Sima Fang ordered Sima Lang to bring the Sima family out of Luoyang and return to their ancestral home in Wen County, Henei Commandery. Some months later, as Sima Lang foresaw that chaos would break out in Henei Commandery, he relocated his family to Liyang Commandery (黎陽郡; around present-day Xun County, Henan), where they stayed with Sima Lang's kinsman, Zhao Weisun. In 194, when war broke out between the warlords Cao Cao and Lü Bu, Sima Lang brought his family out of Liyang Commandery and again returned to their now-ravaged ancestral home in Wen County, Henei Commandery, where Sima Yi and his brothers largely sustained themselves by living as farmers; fending off local groups of bandits while studying diligently during their free time.
Around 201, the administrative office of Henei Commandery nominated Sima Yi to serve in the government by holding local office, possibly as a clerk in charge of the records, and in 202 he was sent as a Reporting Officer (上計掾) to the capital. Around the same year, he married a woman named Zhang Chunhua, possibly at the instigation of his father. At the same time, the warlord Cao Cao, who then held the position of Minister of Works in the Han imperial court, heard of Sima Yi's talent and wanted to recruit him to serve in the administration. Sima Yi declined, presumably on grounds of illness, with the Book of Jin more specifically mentioning that he, seeing that the Han Empire's future was bleak, declined and lied by supposedly saying that he suffered from paralysis; staying at home, with Cao Cao's spies reporting that they saw Sima Yi lying motionless in bed.
One day—in a story that may be apocryphal—while Sima Yi was drying his books under the sun, there was a sudden downpour, so he rushed out to grab his books and was seen by a maid. Sima Yi's wife, Zhang Chunhua, feared that the maid would leak out news that Sima Yi was well and get their family into trouble, so she killed the maid to silence her.
When Cao Cao died in Luoyang in March 220, there was apprehension in the imperial court. Sima Yi supervised the funerary arrangements to ensure everything would be carried out in an orderly fashion, and accompanied the funeral cortège to Ye, earning the respect of officials within and outside the central government.
Advising Cao Cao to attack Yi Province
In 215, Sima Yi accompanied Cao Cao on his campaign against the warlord and Taoist religious leader Zhang Lu, whom Cao Cao defeated at the Battle of Yangping in Hanzhong Commandery. Afterwards Sima Yi urged him to capitalise on the momentum and attack his rival Liu Bei, who was in the neighboring Yi Province. Sima Yi said because Liu Bei had only recently seized control of Yi Province from Liu Zhang, he had yet to establish a strong foothold in the province. Cao Cao rejected Sima Yi's idea and said he was already content with having Longyou (隴右; covering parts of present-day Gansu and Shaanxi). He then turned his attention to his other key rival Sun Quan.
Urging Cao Cao to usurp the throne
Sun Quan sent an emissary to meet Cao Cao, asking to make peace and expressing his willingness to pledge allegiance to Cao Cao. He also urged Cao Cao to seize the throne from Emperor Xian and declare himself emperor. In response to Sun Quan's suggestion, Cao Cao remarked; "This kid wants me to put myself on top of a fire!" Sima Yi told him: "The Han dynasty nears its end. Your Lordship controls nine-tenths of the Han Empire. You are in a position to take the throne. Sun Quan's submission is the will of Heaven." Previously, during Yu's time and throughout the Xia, Yin, and Zhou dynasties, the rulers who did not hesitate when they should take the throne were the ones who truly understood Heaven's will. Cao Cao did not usurp the throne from Emperor Xian and remained a subject of the Han Empire until his death.