Who is the fourth grandfather who robbed the tomb?

The four founders of grave robbery were Cao Cao, Wu Zixu, Xiang Yu and Sun Dianying.

There are four schools of grave robbery, called the founders. They are Cao Cao, Wu Zixu, Xiang Yu and Sun Dianying. Mojin religion aims at the Book of Changes, determines the location of tombs, and relies on geomantic omen and astrology to rob tombs. The disciple of Mojinmen is named Mojinchang, and the leader is Cao Cao. The disciple of Faqiu School is called Faqiuguan, and the founder of Faqiu School is Wu Zixu. He dug up the tomb of King Chu Ping and whipped the body. The disciple of Xie Ling School was named Xie Ling Lux, and the founder of the school was Xiang Yu. According to historical records, Xiang Yu excavated the most famous mausoleum, the Mausoleum of Qin Shihuang. The disciples of Yishan Sect are called Yishan people. Disciple Sun Dianying robbed Ganlong Mausoleum and Cixi Mausoleum under the guise of military exercises.