Why is Bao Zheng called Panther Charcoal?

Bao Zheng (May 28th, 999-1July 3rd, 062), also known as Bao, was born in Hefei, Luzhou (now Feidong, Anhui). He was an official in the Northern Song Dynasty and was famous for his honesty. Renzong Tiansheng Dynasty Jinshi. Tired of mobile surveillance empire, it is suggested to train and select generals and enrich border reserves. He has served as a judge in three divisions and a transshipment ambassador in JD.COM, Shaanxi and Hebei. Later generations regarded him as a god, regarded him as the reincarnation of Wenquxing, and became Yan Luowang, the fifth hall of hell after his death. Its black face image is also called "Bao Qingtian", "black spot" and "black charcoal".