Billionaire T. Boone Pickens, the one-time wildcat Texas oil prospector who built an energy empire during a 65-year career, and whose personality was as outsized as the state he called home, died Wednesday at 91.

The energy industry pioneer, philanthropist and hedge fund magnate whose boardroom brawls, corporate raiding and oil booms and busts became the stuff of legend died of natural causes surrounded by friends and family, spokesman Jay Rosser said in a statement from Pickens’s foundation.

The “oracle of oil” vaulted to prominence in the 1980s, along with other brass-knuckles corporate titans such as Carl Icahn.

Pickens made the cover of Time Magazine in 1985 as a “corporate raider” after his Mesa Petroleum bought shares in Gulf Oil and began pressuring the company to restructure itself and boost shareholder returns.

Gulf was later sold to Chevron, netting Mesa a huge payday.

The strategy has since become commonplace on Wall Street, though today’s billionaire shareholder critics are usually called “activists” and not “raiders” because there is less talk of completely taking over a company.

As a young man Pickens worked for Phillips Petroleum before striking out on his own, using $2,500 of borrowed money to launch Petroleum Exploration Inc.

It was a predecessor company to Mesa Petroleum, which he took public in 1964 and built into one of the country’s largest independent oil and gas firms.

Pickens founded BP Capital when he was in his late 60s in 1997 and rode the fund to great riches in oil and gas price movements.

In 2008 he called for a shift away from oil to renewable energy and natural gas, which he championed as a “bridge fuel” to a non-fossil fuel future, in part to reduce the flow of funds to OPEC nations, but also as a nod to environmental concerns.

Pickens was a longtime Republican political donor. He did not hesitate to use his fortune to sully John Kerry’s Vietnam war record, funding attack ads by the group Swift Boat Veterans for Truth that helped sink Kerry’s 2004 presidential bid.

In 2016 Donald Trump’s presidential campaign received a boost when Pickens shifted his support from Jeb Bush to Trump, and agreed to help convince other wealthy donors to contribute to the brash New York property tycoon.

On Wednesday Republican Senator Ted Cruz of Texas hailed Pickens as “a great philanthropist and an energy innovator who promoted many commonsense solutions to make America energy independent.”

Pickens, a longtime fitness enthusiast, earned a reputation for aphorisms that became known as Boone-isms.

In 2012 he had a memorable exchange with the rapper Drake, nearly six decades his junior.

When Drake tweeted that “the first million is the hardest,” Pickens replied: “The first billion is a helluva lot harder.”