Mr Pickens was known for his activism on behalf of shareholders. : US businessman T Boone Pickens, a Texas energy investor known for his folksy speech and ruthless business practices, has died at age 91. Mr Pickens, whose activism on behalf of shareholders was legendary, closed his BP Capital energy hedge fund last year, citing declining health. Mr Pickens was a well-known business personality. An early practitioner of activist investing, he launched campaigns against established oil companies and others that made him a household name in the 1980s.