Guo Si () (died 197), also known as Guo Duo, was a Chinese military general, politician, and warlord serving under the warlord Dong Zhuo during the late Eastern Han dynasty of China. He assisted Dong Zhuo in his many campaigns and served as a subordinate of Dong Zhuo's son-in-law, Niu Fu, after Dong Zhuo relocated the imperial capital to Chang'an. He later became one of the de facto regents of Emperor Xian, wherein they occupied the capital and held the emperor and imperial officials hostage. However, his downfall came when he quarrelled with his co-regent, Li Jue. He and Li Jue were ultimately defeated by Yang Feng and Dong Cheng, who assisted the emperor to flee the capital. Guo Si was eventually betrayed and murdered by one of his subordinates. Early to mid-career As an early supporter of Dong Zhuo, he participated in most of Dong Zhuo's major battles, including the subjugation of the Yellow Turban rebels, the battle of Liang Province, and the war with the coalition against Dong Zhuo. At the start of the war with the eastern warlords, Guo Si was sent to assist Niu Fu to improve the defences of Mei County. They built up fortifications and stored 30 years of food supply there before Dong Zhuo moved the capital to Chang'an from Luoyang. After Hu Zhen and Lü Bu suffered a major defeat at the hands of Sun Jian and Dong Zhuo's retreat to Chang'an, Niu Fu, Guo Si and Li Jue were ordered to station themselves in Shan (present-day Shaanxi), which was the battle front against the anti-Dong-Zhuo coalition. At the time the alliance was having internal conflicts and did not focus on fighting Guo Si and Li Jue, so the senior general Zhu Jun could only ask his old friend, Tao Qian to give him a hand in a futile effort to fight the forces of Dong Zhuo. Tao Qian, despite having a general alliance with Dong Zhuo, sent 3,000 elite Danyang troops to help Zhu Jun in his battle against Guo Si and Li Jue at Zhongmu County, where Zhu Jun was totally crushed. Guo Si, Li Jue and Zhang Ji then carried out raids in the Chenliu and Yingchuan commanderies, which Cao Cao was unable to stop and many residents there were captured and enslaved. Battle of Chang'an Because he was stationed outside the capital, Guo Si was able to return