According to legend, in the battle between Chu and Han, Liu Bang, Emperor Gaozu, took the lead in commanding the battle in a carriage driven by two people in those years when he was at war with Xiang Yu, the overlord of Western Chu. There are three seats in the carriage. The first two seats are drivers, followed by Liu Bang. The coachman who drives the carriage is divided into "right horse" and "assistant horse", one is right horse and the other is right horse, and drives the carriage in turn.

One day, Liu Bang and Xiang Yu fought fiercely at the junction of Fengxian and Peixian counties in Xuzhou for three days and three nights. Finally, Liu Bang fled. Xiang Yu pursued the victory and pursued it. At this point, Liu bang only had a coachman and a dozen soldiers, and Xiang Yu's military forces were about to catch up. At this time, Zheng Ma was unfortunately shot by random arrows and died on the spot. The assistant horse immediately sat in Zheng Ma's seat and drove the carriage forward. At this critical moment, the assistant horse took off his red robe and put on Liu Bang's yellow robe. When the carriage came to a corner, Liu Bang jumped out of the carriage.

Xiang Yu's soldiers have always regarded the yellow robe as Liu Bang and tried their best to catch up. When they caught up with the carriage, it was empty except for a yellow robe. The auxiliary horse jumped off at another corner and ran away.

Later, Liu Bang became emperor. In order to repay the vice horse for saving his life, he posted royal lists everywhere to find the vice horse. After the deputy horse was found, the official was a surname, and Liu Bang betrothed his daughter to him, which was called "the deputy horse's surname". Because "Deputy Horse" is indecent, people call it "Xu surname". Later, people also removed the word "surname" and called it "Ma Xu". Since then, Ma Xu has become synonymous with the emperor's husband.