Cao Bao (died 196) was a military officer serving under Tao Qian, the Governor of Xu Province, during the late Eastern Han dynasty of China.
An annotation from the Yingxiong Ji (英雄記; "Records of Heroes", authored by Wang Can) 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 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).
"[4] 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.
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.