Cao Zheng, nicknamed "Knife Ghost". He was born in a family of butchers, so he was proficient in the technique of killing pigs and cattle, and was known as the "knife ghost". Cao Zheng once worked for a rich man, but because he lost his capital by doing business for the rich man, he had no choice but to become the son-in-law of a farmer near Huangnigang.
Cao Zheng's story is related to Yang Zhi and Lu Zhishen. After Yang Zhi was robbed of the Birthday Gang in Huangnigang, he fled to Cao Zheng's hotel, where he clashed with Cao Zheng because he had no money to pay the bill. But the two didn't know each other if they didn't fight, and Yang Zhi was finally taken in by Cao Zheng. Yang Zhi later took refuge in Erlongshan and met Lu Zhishen. Cao Zheng used a trick to send Yang Zhi and Lu Zhishen to Erlong Mountain and helped them capture the cottage.
Cao Zheng later returned to Liangshan with Yang Zhi, Lu Zhishen, Wu Song, Shi En and others. In Liangshan, Cao Zheng was responsible for slaughtering cattle, horses, pigs, sheep and other livestock, and was the eighty-first hero of Liangshan. In the follow-up story of "Water Margin", Cao Zheng died in the battle against Fang La.
Although the image of Cao Zheng is not the main character in "Water Margin", his story shows the spirit of unity and mutual assistance of the heroes of Liangshan, as well as the difficulties and struggles they faced in feudal society. Cao Zheng's image also reflects the hard life of the people at the bottom of society at that time and their spirit of fighting for survival.