The BBC has uncovered how a Chinese national, known in criminal circles as 'Fentanyl King' Brother Wang, became a major figure in Mexico's fentanyl trade. The US Department of Justice identifies him as 39-year-old Zhang Zhidong.

Zhang Zhidong, described as the 'Mexican king' of fentanyl, has been accused in the United States of supplying the deadly drug. He allegedly played a key role in sourcing precursor chemicals from China for fentanyl production in Mexico, also linked to 1000 kg of cocaine and 1800 kg of fentanyl.

Zhang Zhidong, a Chinese university graduate, has been accused of becoming a "fentanyl king" for a Mexican cartel. He is charged with leading a global drug trafficking and money laundering operation.