Zhou Yu
In Chapter 45, Jiang Gan volunteers to persuade Zhou Yu to surrender to Cao Cao and travels to Zhou Yu's camp. Zhou Yu knows Jiang Gan's true purpose of the visit, so he tricks Jiang Gan into believing that two of Cao Cao's naval commanders (Cai Mao and Zhang Yun) are planning to assassinate their lord and defect to his side. Jiang Gan also gets hold of a letter apparently written by Cai Mao and Zhang Yun to Zhou Yu, in which they claimed that they will kill Cao Cao soon and present his head to Zhou Yu. He then steals the letter while Zhou Yu is asleep, returns to Cao Cao's camp, and shows Cao Cao the letter. The letter is actually a fake letter written by Zhou Yu. Cao Cao falls for the ruse and orders Cai Mao and Zhang Yun to be executed. He realises his folly later but it is too late already.