T Boone Pickens Jr, an oil prospector and pioneer in hostile takeovers whose folksy wit made him one of America’s most recognizable business leaders, has died at age 91.

Pickens rose to fame as founder and chief executive of Mesa Petroleum, where he was an advocate for shareholder rights who liked to vilify the excesses of “Big Oil”. He later morphed into a high-stakes energy trader before becoming a philanthropist and early investor in renewable power.