| Tao Qian, Liu Bei, Cao Cao|Cao Bao Wikipedia
Cao Bao (died 196) was an officer serving under Tao Qian, the Governor (牧) of Xu Province, in the late Eastern Han dynasty. He became a subordinate of Tao Qian's successor, Liu Bei, after Tao's death in 194. He was killed by Zhang Fei in 196 after a quarrel.
The only known information about Cao Bao in history comes from Pei Songzhi's annotations to Chen Shou's Records of the Three Kingdoms (Sanguozhi), which recorded the history of the late Eastern Han dynasty and the Three Kingdoms period.
An annotation from the Yingxiong Ji (英雄記) in the Sanguozhi recorded:
Liu Bei left Zhang Fei behind to defend Xiapi (下邳; Xu Province's capital) and led his troops to battle Yuan Shu at Shiting (石亭) and Huaiyin (淮陰). Cao Bao, a former officer under Tao Qian, remained in Xiapi. Zhang Fei wanted to kill Cao Bao (for reasons unknown). Cao Bao fled back to his own camp and strengthened his defences while sending a messenger to request aid from Lü Bu (who was taking shelter under Liu Bei then). Lü Bu attacked Xiapi and defeated Zhang Fei and drove him away.
Another annotation, also from the Yingxiong Ji, in the Sanguozhi, recorded a different account:
[...] Xu Dan (許耽), who was from Danyang (丹楊) and was serving as a General of the Household (中郎將) under Liu Bei, sent a Major (司馬) Zhang Kuang (章誑) to meet Lü Bu at night. Zhang Kuang told Lü Bu, "Zhang Yide (Zhang Fei) quarrelled with Cao Bao, the Chancellor (相) of Xiapi, and then killed him. The city is now in a state of chaos. [...]"
Sima Guang used the second account when he compiled the Zizhi Tongjian.
Cao Bao's conflict with Zhang Fei was dramatised in the historical novel Romance of the Three Kingdoms by Luo Guanzhong.
In the novel, Cao Bao was Lü Bu's father-in-law. He was coerced by Zhang Fei to drink wine even though he insisted that he abstained from alcohol. When Cao Bao pleaded with Zhang Fei to stop forcing him to drink by asking the latter to "spare him in consideration of his son-in-law", Zhang became furious because he hated Lü Bu. He ordered his men to flog Cao Bao 50 times and only gave up when the other officers begged him to stop. Cao Bao bore a grudge against Zhang Fei for the beating, so he secretly contacted Lü Bu and assisted his son-in-law in seizing control of Xiapi. Zhang Fei was drunk when Lü Bu attacked the city so he lost the battle and fled from Xiapi. Cao Bao led about a hundred soldiers to pursue Zhang Fei but ended up being killed by the latter.