Biography
Xu was a native of Yingchuan (present-day Xuchang, Henan). As a youth, he enjoyed practising swordplay. Between 190 and 193, Xu and his friend Shi Tao (石韜) travelled south to Jing Province, where they met and befriended Zhuge Liang and Pang Tong. The 3 of them studied in the same school during this period.
Xu was reciting a poem in the streets one day, and was overheard by Liu Bei. Liu Bei impressed by his poems recruited him. Xu came to serve Liu Bei when the latter was residing in Xinye, under the warlord Liu Biao of Jing Province. Around 208, Liu Biao died and was succeeded by his son, Liu Cong. Cao Cao's forces invaded Jing Province and Liu Cong surrendered to Cao. Liu Bei was forced to flee southward, accompanied by Xu. However, during the chaos, Xu's mother was captured by Cao Cao's troops. Cao Cao used Xu's mother to bring Xu to his side. Xu decided to leave Liu Bei to go see his mother. However, Xu promised Liu Bei not to help Cao Cao. He also told Liu Bei about his classmate Zhuge Liang, and mentioned that Zhuge Liang is more capable then himself. He also revealed the location of Zhuge Liang to Liu Bei.
In 220, Cao Cao died and was succeeded by his son Cao Pi, who forced Emperor Xian of Han to abdicate in his favour, marking the start of the Cao Wei dynasty. Cao Pi appointed Xu as Right General of the Household (右中郎將) and Imperial Secretary (御史中丞).
Between 228 and 234, Zhuge Liang launched a series of Northern Expeditions against the state of Cao Wei. When Zhuge heard that Xu was serving in Cao Wei, he sighed, "Wei has so many capable people! Why don't I see those two men have their talents put to use?" (The two men refer to Xu Shu and Shi Dao.) Xu eventually died of illness.
Read more about this topic: Xu Shu