In classic wildcatter style, Mr. Pickens’s fortunes rose to prodigious heights and then collapsed, only to resume their roller coaster course in later years. At the apex of his fame and fortune, in the mid-1980s, he appeared on the covers of national magazines, owned vast ranches and crisscrossed the country on corporate jets belonging to Mesa. He founded and headed the United Shareholders Association to lobby for more rights for ordinary shareholders and against legislation aimed at thwarting corporate raiders like him.

Then, in the 1990s, the Pickens cult collapsed. He borrowed excessively to expand Mesa’s natural gas production. But gas prices failed to rise, and as Mesa’s share price plummeted, the company became a target for corporate raiders. When he sought to save Mesa from a hostile takeover by poison pill tactics, he was denounced as a hypocrite in the press and even by members of his United Shareholders. He ended up being forced out of Mesa.

But a decade later, Mr. Pickens was again riding high. By 2002, thanks to a commodities fund he headed, his personal fortune climbed past $200 million, more than he was worth during his corporate-raiding heyday. He had also shed his old populist image and embraced the conservative Republican cause. During the 2004 presidential campaign that led to George W. Bush’s re-election, Mr. Pickens helped finance attacks on the Vietnam War record of Senator John Kerry, Mr. Bush’s opponent.

By 2010, when he was past 80, Mr. Pickens had become a billionaire by running a natural gas-oriented hedge fund, BP Capital. He closed it down in January 2018 because of ill health and the fund’s poor performance.

Mr. Pickens also headed a nationwide campaign to push for energy self-sufficiency through the exploitation of natural gas, wind power and solar energy with the aim of reducing the United States’ dependence on oil imports from the Middle East.

“We’re infidels with most of these people, and they have no use for us,” he told The New York Times in 2010. He gained the backing of some environmentalists and liberal Democrats.