There are two reasons. One is the pronunciation of wild boar skin, which means Nurhaci in Mongolian. The other is representing wild boar, which is a symbol of bravery. This is also a satire on Nurhachi at that time, because Nurhaci at that time was extremely ferocious, like a wild boar.
Wild boars were very ferocious animals in ancient times. At that time, people did not have as many defense tools as we do now, so sometimes wild boars would come and eat the crops that people planted when they had nothing to eat, but people had nothing to do with them. , so in ancient times, describing a person as a wild boar was actually a very bad evaluation. The reason why people described Nurhaci in this way was that when Nurhachi founded Houjin, he did a lot of things that made people angry, so he got such an evaluation.
When Nurhachi founded Houjin, he wronged his ancestors and killed them. Even now, this matter is unacceptable. The least thing a person can do is not Forgetting his roots, he couldn't do anything to his elders even if it was a big deal. He directly killed his ancestors. This is not an exaggeration even if he gets a thousand years of infamy.
Furthermore, every time Nurhachi captured a city, he would kill slowly. He would not peacefully deal with the people and prisoners of war in the city, but would go on a killing spree, killing the Han people and forcing the Han people to join the Manchus. How could the Han people not hate him? Also, the Manchu Qing Dynasty did not work hard at all. They actually implemented a policy of seclusion and cultural inquisition. As a result, the development of the entire country plummeted, and people's living standards fell back. His rule did not make any contribution to the country. His good contributions made his development worse and worse, so people called him derogatory terms like boar skin.