Chen Gong
Cao Cao's father Cao Song was killed in autumn 193 by troops of Tao Qian, governor of Xu Province (who claimed to be innocent, and that Cao Song's murderers had been mutineers). Enraged, Cao Cao massacred thousands of civilians in Xu during two punitive expeditions in 193 and 194, to avenge his father. Because he took the bulk of his soldiers to Xu Province in order to defeat Tao Qian, most of his territory was left undefended. A number of discontented officers led by Chen Gong and Zhang Chao plotted to rebel. They convinced Zhang Miao (Zhang Chao's brother) to be their leader, and to ask Lü Bu to come with reinforcements. Chen Gong invited Lü Bu to be the new Inspector of Yan province. Lü Bu accepted this invitation and led his soldiers into the province. Since Cao Cao's army was away, many of the local commanders figured that fighting would be a lost cause and surrendered to Lü Bu as soon as he arrived. However three counties – Juancheng, Dong'a, and Fan, remained loyal to Cao Cao and when Cao Cao returned, he gathered his own forces at Juancheng.