Jia Xu (147 – 11 August 223),^{[lower-alpha 1]} courtesy name Wenhe, was an official of the state of Cao Wei during the early Three Kingdoms period of China.^[1] He started his career in the late Eastern Han dynasty as a minor official. In 189, when the warlord Dong Zhuo took control of the Han central government, he assigned Jia Xu to the unit led by Niu Fu, his son-in-law. In May 192, after Dong Zhuo was assassinated by Lü Bu, Jia Xu advised Li Jue, Guo Si and Dong Zhuo's loyalists to fight back and seize control of the imperial capital, Chang'an, from a new central government headed by Lü Bu and Wang Yun. After Li Jue and the others defeated Lü Bu and occupied Chang'an, Jia Xu served under the central government led by them. During this time, he ensured the safety of the figurehead Han emperor, Emperor Xian, who was being held hostage by Li Jue. He also attempted to prevent internal conflict between Li Jue and Guo Si, but with limited success. After Emperor Xian escaped from Chang'an, Jia Xu left Li Jue and briefly joined the general Duan Wei before becoming a strategist of the warlord Zhang Xiu. While serving under Zhang Xiu, he advised his lord on how to counter invasions by the warlord Cao Cao, who had received Emperor Xian in 196 and taken control of the central government. In 200, during the Battle of Guandu between Cao Cao and his rival Yuan Shao, Jia Xu urged Zhang Xiu to reject Yuan Shao's offer to form an alliance and instead surrender to Cao Cao. Zhang Xiu heeded his advice. Jia Xu then became one of Cao Cao's strategists.

During his service under Cao Cao, Jia Xu made three important contributions. First, during the Battle of Guandu, he urged Cao Cao to switch from being on the defensive to adopting an offensive stance, which ultimately led to Cao Cao's decisive victory over Yuan Shao. Second, during the Battle of Tong Pass in 211, he suggested to Cao Cao to pretend to agree to make peace with the northwestern warlords Han Sui and Ma Chao, and then sow discord between them. Cao Cao heeded his suggestion, successfully stirred up internal conflict among the warlords, and then used the opportunity to defeat them. Thirdly, in the 210s, when Cao Cao's sons Cao Pi and Cao Zhi were fighting to be their father's successor, Jia Xu indirectly helped Cao Pi by giving him advice and hinting to Cao Cao that he should choose the older son to be his heir apparent. After Cao Cao's death in 220, Cao Pi ended the Eastern Han dynasty by forcing Emperor Xian to abdicate the throne to him, and founded the state of Cao Wei with himself as the emperor. As an expression of gratitude to Jia Xu, Cao Pi appointed him as Grand Commandant – one of the top three positions in the Wei government – and promoted him to a district marquis. Between 220 and 223, Jia Xu advised Cao Pi against attacking Cao Wei's rival states, Eastern Wu and Shu Han, and focus on internal development. However, Cao Pi ignored his advice and invaded Wu, but ended up sustaining heavy losses and not making any significant gains. Jia Xu died in 223.

Jia Xu was from Guzang County (姑臧縣), Wuwei Commandery (武威郡), which is in present-day Wuwei, Gansu. In his youth, he was unimpressive and unheard of. However, Yan Zhong (閻忠), an official from Hanyang Commandery (漢陽郡; around present-day Gangu County, Gansu), felt that Jia Xu was extraordinary and even remarked that Jia had the brilliance of Zhang Liang and Chen Ping, two famous strategists of the early Western Han dynasty.^{[Sanguozhi 3]}

Jia Xu was nominated as a xiaolian to serve in the Eastern Han government as a Gentleman Cadet (郎). However, due to illness, he quit his job and went home. On the way back, he was captured by Di rebels at Qian County (汧縣; in present-day Long County, Shaanxi) along with several other travellers. He told the rebels: "I am a maternal grandson of Lord Duan. If you let me live, my family will reward you handsomely." "Lord Duan" referred to Duan Jiong (段熲), who held the position of Grand Commandant (太尉) in the Han imperial court. As Duan Jiong had served for years as a general guarding the Han Empire's western regions, he was well known among the people living in the area. Jia Xu knew that the Di rebels were afraid of Duan Jiong, so he pretended to be Duan Jiong's maternal grandson. As he expected, the rebels treated him respectfully and released him. The other travellers were all killed.^{[Sanguozhi 4]}

In 189,^[2] the warlord Dong Zhuo entered the imperial capital, Luoyang, and took control of the central government. Jia Xu was then serving as the Commandant (都尉) of Pingjin (平津) and an assistant official in the Grand Commandant's office. He was promoted to Colonel Who Attacks Barbarians (討虜校尉) and assigned to the unit led by Dong Zhuo's son-in-law, Niu Fu.^{[Sanguozhi 5]}

In 192,^[3] Dong Zhuo was assassinated by Lü Bu in the imperial capital, Chang'an,^{[lower-alpha 2]} while Niu Fu was murdered by his subordinates.^[3] The rest of Dong Zhuo's loyalists, including Li Jue, Guo Si and Zhang Ji, became fearful and wanted to disband and return to their respective home commanderies. Jia Xu told them: "I heard that the new government in Chang'an is planning to exterminate everyone from Liang Province.^{[lower-alpha 3]} If all of you break up and travel alone, even a tingzhang^{[lower-alpha 4]} can arrest you. Why don't you retreat to the west together? There you can gather and reorganise your forces, and then attack Chang'an to avenge Lord Dong. If you succeed, you can make use of imperial authority to conquer the rest of the Empire. If you fail, it's still not too late to escape." Dong Zhuo's loyalists agreed with Jia Xu and did as he suggested. They managed to defeat the new central government in Chang'an led by Lü Bu and Wang Yun, and then took control of the city.^{[Sanguozhi 6]}

Pei Songzhi, who annotated Jia Xu's biography in the Sanguozhi, strongly criticised Jia Xu for offering this suggestion. He argued that Dong Zhuo's death marked the end of his tyranny and a possible revival of the declining Eastern Han dynasty. However, due to Jia Xu's suggestion, the Han Empire became even more chaotic after Dong Zhuo's death.^{[Sanguozhi zhu 1]}

When Jia Xu later served as Left Adjunct (左馮翊), Li Jue and Dong Zhuo's loyalists wanted to reward him by making him a marquis, but Jia Xu said, "That suggestion I made was meant to save your lives. What merit have I achieved to deserve a reward?" He declined to accept the marquis title. Later on, when he was nominated to serve as a Supervisor of the Masters of Writing (尚書僕射), he said: "The Supervisor of the Masters of Writing is like a tutor to officials. I don't have a strong reputation so I am afraid I might not be able to convince people that I am suited for this appointment. What will become of the imperial court if I accept this appointment for my personal glory?" He was then assigned to be a Master of Writing (尚書) instead, and was tasked with selecting candidates to serve in the government. Li Jue and the others regarded him highly but were also wary of him.^{[Sanguozhi 7]} The candidates Jia Xu chose tend to be officials who formerly served in the previous administration. Jia Xu was praised for this mode of selecting government officials by retaining some continuity in appointments.^{[Sanguozhi zhu 2]} When there were tensions between Li Jue, Guo Si and Fan Chou, with their respective subordinates urging them to go to war, Jia Xu reprimanded them for their behaviour and tried to persuade them to avoid conflict. They listened to him.^{[Sanguozhi zhu 3]}

When his mother died, Jia Xu resigned and went home for filial mourning. He was given the honorary position of a Household Counsellor (光祿大夫) by the imperial court. In 195,^[4] when conflict broke out between Li Jue and Guo Si in Chang'an, Li invited Jia Xu back to serve as General Who Upholds Righteousness (宣義將軍).^{[Sanguozhi 8]} Li Jue and his men discussed with Jia Xu their plan to bring Emperor Xian to their camp and use the emperor as a hostage to threaten Guo Si, but Jia Xu said: "No, it isn't right to hold the Emperor hostage." Li Jue refused to listen to him and went ahead. Guo Si, on the other hand, kidnapped Emperor Xian's subjects and held them hostage in his own camp.^[4] Zhang Xiu told Jia Xu, "You shouldn't stay here any longer. Why don't you leave?" Jia Xu replied, "I have received grace from the Empire, so I won't betray the Empire's trust in me. If you wish to leave, you can go. I won't leave."^{[Sanguozhi zhu 4]}

Li Jue used material wealth to tempt thousands of Qiang tribesmen to support him in his struggle against Guo Si. He even promised to give palace women as concubines to the tribal chiefs. When the tribesmen showed up at Chang'an, they asked: "Is the Emperor inside? General Li has promised to give us palace women as concubines. Where are they?" Emperor Xian turned to Jia Xu for help. Jia Xu secretly hosted a banquet for the tribal chiefs, gave them some expensive material gifts, and succeeded in making them leave. Li Jue lost the support of the tribal chiefs.^{[Sanguozhi zhu 5]} Jia Xu played an important role in resolving the conflict between Li Jue and Guo Si, and in ensuring Emperor Xian's safety during the time.^{[Sanguozhi 9]} Later, after Emperor Xian escaped from Chang'an, Li Jue led his forces in pursuit and defeated forces led by the emperor's loyalists. He hated certain officials such as Zhao Wen (趙溫), Wang Wei (王偉), Zhou Zhong (周忠) and Rong Shao (榮邵), and wanted to execute them. Jia Xu advised him against it by saying: "They are the Emperor's subjects. How can you harm them?" Li Jue spared them.^{[Sanguozhi zhu 6]}

After Emperor Xian left Chang'an, Jia Xu gave up his official post and left Li Jue. He heard that the general Duan Wei (段煨), who was from the same commandery as him, was stationed at Huayin County (華陰縣; present-day Huayin, Shaanxi), so he went to Huayin County to join Duan Wei. Jia Xu was well known among Duan Wei's men, so Duan Wei was fearful that Jia Xu would seize the position of leadership from him. He pretended to treat Jia Xu respectfully while secretly keeping a close watch on him. Jia Xu knew that Duan Wei was suspicious of him, and he felt very uneasy.^{[Sanguozhi 10]}

Around 196,^[5] the warlord Zhang Xiu was based in Nanyang Commandery (南陽郡; around present-day Nanyang, Henan). Jia Xu secretly contacted Zhang Xiu and conveyed his intention to join him; Zhang Xiu agreed and sent his men to receive Jia Xu. Before Jia Xu left Duan Wei, someone asked him, "(Duan) Wei treated you generously. Why are you leaving?" Jia Xu replied, "(Duan) Wei is suspicious by nature and he's wary of me. Even though he treats me generously now, I believe he will harm me eventually. However, if I leave now, he will be more than happy to see me gone. If I manage to help him find an external ally, he will treat my family well. (Zhang) Xiu lacks a strategist, so he definitely hopes to have me on his side. By leaving, I can protect myself and my family."^{[Sanguozhi 11]}

Jia Xu left Duan Wei and headed to Nanyang Commandery, where Zhang Xiu welcomed him and treated him like a family elder. As Jia Xu foresaw, Duan Wei was pleased to see that Jia Xu had not only left, but also helped him gain Zhang Xiu as an ally. Jia Xu urged Zhang Xiu to form an alliance with Liu Biao, the Governor of Jing Province,^{[Sanguozhi 12]} and went to speak to Liu Biao. Liu Biao treated him like an honoured guest. Jia Xu remarked: "(Liu) Biao has the ability to serve as a Ducal Minister in times of peace. However, he not only lacks foresight, but is also suspicious and indecisive, hence he won't be successful."^{[Sanguozhi zhu 7]}

Cao Cao was very pleased to see Jia Xu. He held Jia Xu's hand and said: "You are the person who helps to make my trustworthiness known throughout the Empire." Jia Xu was appointed Bearer of the Mace (執金吾) and enfeoffed as a Marquis of a Chief Village (都亭侯). He was later promoted to the position of Governor (牧) of Ji Province. As Ji Province was still under Yuan Shao's control then, Jia Xu served as a military adviser to Cao Cao, who then held the appointment of Minister of Works (司空).^{[Sanguozhi 16]}

On 6 April 220, while Cao Pi was still King of Wei, Jia Xu was appointed as Grand Commandant (太尉).^{[Sanguozhi 24]} In late 220, Cao Pi forced Emperor Xian to abdicate the throne to him, thus ending the Han dynasty. He then established the state of Wei with himself as its first emperor.^[10] After ascending the throne, Jia Xu remained as Grand Commandant; he was also promoted from a Marquis of a Chief Village to the Marquis of Weishou District (魏壽鄉侯), with a marquisate of 800 taxable households.^{[Sanguozhi 25]} Jia Xu's promotion was allegedly an expression of gratitude from Cao Pi, who wanted to thank him for helping him seize the succession years ago.^{[Sanguozhi zhu 9]} Sun Quan laughed when he heard that Cao Pi had appointed Jia Xu as his Grand Commandant.^{[Sanguozhi zhu 10]}

According to the Xin Tang Shu, Jia Xu descended from the royal family of the Zhou dynasty. His ancestor was Gongming (公明), the youngest son of Shuyu (a son of King Wu of Zhou). Gongming was enfeoffed by King Kang of Zhou as the Count of Jia (賈伯) and given the lands around Linfen as his fief, which was named "Jia". His descendants adopted "Jia" as their family name. Jia Yi, a notable scholar-politician who lived in the Western Han dynasty, was an ancestor of Jia Xu. Jia Xu's father, Jia Gong (賈龔), served as a General of Light Cavalry (輕騎將軍) in the Eastern Han dynasty and moved his residence to Wuwei Commandery, where Jia Xu was born. Jia Xu had an elder brother, Jia Cai (賈綵).^[11]

Jia Xu had at least three sons. His eldest son, Jia Mu (賈穆), was a Chief Commandant of Escorting Cavalry (駙馬都尉). After Jia Xu's death, Jia Mu inherited his father's marquis title, Marquis of Weishou District (魏壽鄉侯). He also served as the Administrator (太守) of various commanderies.^{[Sanguozhi 30]} Jia Xu's youngest son, Jia Fang (賈訪), was given a marquis title and 200 taxable households around the same time as when Jia Xu was enfeoffed as the Marquis of Weishou District.^{[Sanguozhi 31]} According to the Xin Tang Shu, Jia Xu had a son, Jia Ji (賈璣), who also served as a Chief Commandant of Escorting Cavalry like Jia Mu, and held the title of a Secondary Marquis (關內侯).^[12] Jia Ji is not mentioned in Jia Xu's official biography in the Sanguozhi.

When Jia Mu died, his marquis title was passed on to his son, Jia Mo (賈模).^{[Sanguozhi 32]} According to the Shiyu (世語), Jia Mo served as a Regular Mounted Attendant (散騎常侍) and General Who Protects the Army (護軍將軍) during the reign of Emperor Hui in the Western Jin dynasty. Jia Mo had two sons, Jia Yin (賈胤) and Jia Kan (賈龕). Jia Yin, Jia Kan, and their cousin Jia Pi, served in the Jin government and held high official positions.^{[Sanguozhi zhu 11]}

Jia Xu annotated the military treatise Wuzi and wrote another military text called Wu Sun Zi Sanshi'er Lei Jing (吳孫子三十二壘經).^[13] He also created a copy of Sun Tzu's The Art of War.^[14]

Chen Shou, who wrote Jia Xu's biography in the Sanguozhi, appraised him as follows: "Xun You and Jia Xu were very detailed in their strategising and had never miscalculated before. However, in terms of adaptability and flexibility, they were second to (Zhang) Liang and (Chen) Ping."^{[Sanguozhi 33]}

Pei Songzhi, who annotated the Sanguozhi, disagreed with Chen Shou. He believed that biographies should be categorised in the same volume on the basis of similarities. He argued that Jia Xu's biography should be in the same volume as the biographies of Cheng Yu and Guo Jia rather than in the same volume as the biographies of Xun Yu and Xun You. In Pei Songzhi's opinion, Jia Xu was more similar to the former two than to the latter two. Pei Songzhi even remarked, "The difference between the moral characters of Xun You and Jia Xu is like the difference between moonlight and candlelight. Both give off light, but they are fundamentally different." He also criticised Chen Shou for appraising Xun You and Jia Xu in the same sentence instead of appraising them separately.^{[Sanguozhi zhu 12]}

Jia Xu was first introduced as a playable character in the seventh instalment of Koei's Dynasty Warriors video game series.

• Lists of people of the Three Kingdoms