Fei Yi (died 16 February 253),[a] courtesy name Wenwei, was a Chinese diplomat, military general, politician, and regent of the state of Shu during the Three Kingdoms period of China.

After Liu Shan became emperor in 223, Fei Yi gradually rose to prominence under the regency of Zhuge Liang, the Imperial Chancellor of Shu.

He also played a significant role in the conflict between the Shu general Wei Yan and Zhuge Liang's chief clerk Yang Yi.

His father died when he was still young so he was raised by an older relative Fei Boren (費伯仁), whose aunt was the mother of Liu Zhang,[b] the Governor of Yi Province (covering present-day Sichuan and Chongqing).

[14] Around the autumn of 225,[13] when Zhuge Liang returned from a military campaign against rebels and the Nanman tribes in southern Shu, Fei Yi and many of his colleagues travelled tens of li out of the capital Chengdu to welcome him back.

[13] After Zhuge Liang returned from his southern campaign in 225,[13] he commissioned Fei Yi as a Colonel of Illustrious Trust (昭信校尉) and sent him as Shu's ambassador to Wu.

Sun Quan treated Fei Yi to alcoholic drinks, saw that he appeared drunk, and then bombarded him with a series of questions about current affairs.

[17] Some Wu officials such as Zhuge Ke and Yang Dao (羊衜), who were known for their oratorical talents, attempted to challenge Fei Yi and pose difficult questions to him.

[19] In another instance, Sun Quan instructed his officials: "When the Shu ambassador arrives, all of you just remain seated, continue eating, and don't stand up to greet him."

As the troops gathered at the staging area in Hanzhong Commandery, Zhuge Liang summoned Fei Yi from Chengdu and appointed him as an Army Adviser (參軍).

[24] In his Chu Shi Biao (literally "memorial on the case to go to war"), Zhuge Liang named Fei Yi, Guo Youzhi and Dong Yun as examples of trustworthy, loyal and competent officials who could provide good advice and assist the emperor Liu Shan in governing Shu more effectively.

Apart from serving as an assistant to Zhuge Liang during the military campaigns against Wei, he was also often sent by the Shu government on diplomatic missions to Wu during this period of time.

[27] Wei Yan, a senior Shu general, was on bad terms with Yang Yi, Zhuge Liang's chief clerk.

[28] Zhuge Liang was upset by the lack of harmony between Wei Yan and Yang Yi, but he was unwilling to take sides because he appreciated the talents of both men and needed their help.

After sending his subordinate to find out the situation in the main camp, he was shocked to learn that Fei Yi had lied to him because all the Shu units were preparing to retreat in accordance with Zhuge Liang's final orders.

[31] After returning to Chengdu, Yang Yi thought that he had made great contributions so he strongly believed that he would be chosen to succeed Zhuge Liang as the new head of the Shu government.

As a result, in 235 Yang Yi was demoted to the status of a commoner and exiled to Hanjia Commandery (漢嘉郡; around present-day Lushan County, Sichuan), where he committed suicide later.

[40][41] At the time, as Shu was in a state of war, Fei Yi had numerous issues to attend to on a daily basis given his role as Prefect of the Masters of Writing.

[42] In late October or November 243, Jiang Wan moved from Hanzhong Commandery to Fu County (涪縣; present-day Mianyang, Sichuan) due to poor health.

"[45] In early 244, the Wei regent Cao Shuang led an army to Mount Xingshi (興勢山; located north of present-day Yang County, Shaanxi) and prepared to attack the Shu-controlled Hanzhong Commandery.

In late June or July, while the Wei army was retreating, Fei Yi led the Shu forces to launch a three-pronged attack and inflicted a devastating defeat on the enemy with Cao Shuang barely escaping alive.

[44] After Fei Yi returned to Chengdu from his victory at Mount Xingshi, he was enfeoffed as the Marquis of Cheng District (成鄉侯) as a reward for his achievement.

[53] Throughout their regencies, Jiang Wan and Fei Yi still maintained control over state affairs in Chengdu even though they were away in Hanzhong for extended periods of time.

Frustrated at his failure to assassinate the Shu emperor, Guo Xiu switched his target to the regent Fei Yi instead and succeeded.

[60] The fifth-century historian Pei Songzhi rebutted Cao Fang's imperial decree and argued that Guo Xiu was not a hero and his assassination of Fei Yi was not "in the service of Wei".

Third, from Pei Songzhi's point of view, Liu Shan and Fei Yi were respectively a ruler and a regent of average calibre, so their deaths would not deal significant damage to Shu.

Moreover, with time they became excessive and arrogant, would usurp royal prerogatives, had close ties with vile persons, monopolize power by establishing those of their clique and plotted against the interest of the State.

However, he died at a relatively young age but must have lived at least until April 268 since Luo Xian recommended him during a feast to Sima Yan as a talented individual.

He once warned Fei Yi: "In the past, Cen Peng commanded troops and Lai Xi wielded the staff of imperial authority; both of them were assassinated.

[74] He also recorded that the people of Shu named Zhuge Liang, Jiang Wan, Fei Yi and Dong Yun as the four heroic chancellors of their state.