The retired American superstar could earn hundreds of millions of dollars from a bout, but China’s Zhang sometimes fights for nothing and supports himself by making deliveries on his motorbike.

The 26-year-old bantamweight has recovered from losing three of his first four fights to improve his win-loss-draw record to 14-3-1, with three wins by knockout.

But it is Zhang’s determination to pursue his career despite numerous obstacles that has won him the hearts of Chinese sports fans and the admiration of the wider public.

His story was part of a recent Chinese government-backed documentary film, “Changing China”, which charts the progress of the world’s most populous country through the stoic battles of ordinary young people trying to get by.