Records of the Three Kingdoms
Cao Ren, courtesy name Zixiao, was a younger cousin of Cao Cao. He joined the rising at the start and was known for discipline. He was not kept merely as a kinsman bodyguard. After Red Cliffs he held Jiangling. Zhou Yu attacked, and the armies faced each other for about a year. Cao Ren eventually withdrew, and Nanjun passed into the arrangements of Liu Bei and Sun Quan.
In 219 Guan Yu came north and Cao Ren held Fan. The Han rose, Yu Jin’s seven armies were lost, and the wall stood only a few boards above the water. Some told him to abandon the city. He said a flood that came fast would go fast, and he stayed. Xu Huang relieved him. After Guan Yu withdrew, Fan was still in Wei hands. Under Cao Pi he was grand general and then grand marshal. He died of illness in 223, at fifty-six.
Romance of the Three Kingdoms
In the novel Cao Ren is the clansman who can hold a city. At Jiangling he is locked with Niu Jin and Zhou Yu. At Fan he holds on in the flood and waits for Xu Huang.
The book does not make him always victorious. The stubbornness of the defense matches the histories. When Guan Yu has the bone scraped, Cao Ren’s sector is the city outside.
Reference: Wikipedia · Cao Ren