Legendary oil tycoon and philanthropist T. Boone Pickens passed away peacefully Wednesday of natural causes at the age of 91, according to the Dallas Morning News.

Pickens made his first millions in oil, burnishing an image as a maverick, unafraid to take on giants in the oil patch. Even his name seemed to fit, like central casting’s idea of what an oilman should be named.

Starting in the 1980s, he became known for launching hostile corporate takeover bids that often resulted in a huge payoff. His fortune soared into the billions.

Pickens flirted with the idea of marketing water from West Texas to the state’s metropolitan areas. In a break from his past, he also developed wind farms.

“Ralph Waldo Emerson said, ‘Do not go where the path might lead, but instead go instead where there is no path and leave a trail.’ That was Boone,” said Alan White, a former banker and close friend of Pickens. “Boone was always going some place where there was no path. He left trails all of his life. Many of us had the good fortune of being able to follow along with him.”

“Boone was stubborn. He was tough,” added White. “He had more charisma than anyone I’ve ever known. He was billionaire rich, and he went broke two or three times. But every time that he was knocked down on his knees, he got back up, dusted himself off and went right back at it.”

Jay Rosser, the billionaire’s longtime chief of staff, told Forbes that his boss pledged to donate 90% of his net worth to charity upon his death.

“Bill Gates called asking him to be a member of the Giving Club [where rich people pledge to bequeath the majority of their wealth to philanthropy].” recounted Rosser. “Boone said, ‘Happy to do it.’ Then he invited Bill to join him in his 90% Club. Bill said, ‘No, I’m fine with doing what I’m doing.’ “

A longtime Oklahoma State University supporter, Pickens will be buried at the Karsten Creek Golf Club, home to the school’s golf team.

The Associated Press contributed to this report.