BiographyGuo Si served under Governor of Liang Province Dong Zhuo as a general since around 180 AD, when he quelled an uprising of the Yellow Turbans in Xiliang. He later served in his campaign against Ma Teng and Han Sui, which was a defeat for Dong Zhuo's army. Guo Si took part in the defense of Sishui Gate, Hulao Gate, and Luoyang from the anti-Dong Zhuo Coalition in 190 AD, but he was defeated, and when his lord was slain in a rebellion by Lu Bu in 192 AD, Guo Si and Li Jue fled west. They gathered an army and, joined by Niu Fu, they recaptured the capital of Chang'an from Wang Yun's Forces, slaying Wang Yun and those who had joined his forces.
Guo Si and Li Jue were driven apart by Yang Biao, who plotted to have them kill each other in order for the strong Cao Cao to become the new regent over Emperor Xian of Han. Guo Si was appointed General of the Rear by Emperor Xian and defended the capital ably, but in 196 AD he started a rivalry with Li Jue when it was said that he had an affair with Li Jue's wife. Yang Biao's rumor drove the two apart, and Guo Si attacked the imperial palace, burning it and killing several attendants. Li Jue and Guo Si's rivalry ended when Zhang Ji negotiated peace between them, but Li Jue succeeded in taking the Emperor out of Chang'an. Guo Si executed two guards for letting them pass, as Guo Si had intended to outsmart Zhang Ji and take the Emperor for himself. Yang Fang and Dong Cheng both captured the emperor from him and began to ride to the east of the Huashan Mountains, and Guo Si and Li Jue's attacks failed. Eventually, they were faced with Cao Cao as an enemy after Cao Cao came to the Emperor's assistance, and Cao Cao and Xiahou Dun destroyed their army. Yang Fang and Han Xian's White Wave Bandits, who gave the Emperor protection, were also destroyed when they tried to recapture the emperor in 197 AD, and Cao Cao moved with the Emperor to Xuchang, which became the new capital. In 198 AD, holed up in Chang'an, Guo Si was slain by his own assistant Wu Xi, around the same time as Li Jue's death.