In defiance of US sanctions, one man was for two decades the linchpin of China’s oil dealings with Iran: a hard-drinking trader known as “Crazy Yang”, who came to be regarded as the world’s largest handler of Iranian crude.

The gregarious Yang Qinglong, who has died of cancer in his native Yunnan province aged 63, was known within his circle for his hospitality and for the green army jacket he wore everywhere. But in Washington Zhuhai Zhenrong, the company he founded, was vilified for impeding measures designed to force Tehran to the negotiating table over its nuclear programme.

In 2012, Zhuhai Zhenrong was added to America’s sanctions list for selling petrol and diesel to Tehran, which has long lacked the refining capacity to process its own output. The blacklisting made little difference to Yang or his company, whose only business was with Iran and whose assets were almost exclusively in China. Indeed, many in the Chinese oil industry saw the Iranian imports as a patriotic effort to provide the energy needed for China’s growing economy.