T. Boone Pickens, Texas oil tycoon and corporate raider, 1928-2019

They also lent weight to his own claims, often repeated, that he was in the vanguard of the modern shareholder rights movement, helping to force a revolution in US corporate management.

Alongside names such as Carl Icahn and Ronald Perelman, Pickens was one of a handful of financial pioneers who cut a swath through Wall Street in the first half of the 1980s. Backed by billions of dollars of junk-bond financing whipped up by Michael Milken, these were the people who proved it was possible to take on some of the biggest and most entrenched interests in American business and win.

Among them, Pickens stood out as something special. An oil man with a passion for gambling, he never adopted the mannerisms of the big-city financier, preferring to plan his daring raids from the Texas Panhandle. That added to his self-wrought image as a champion of the small shareholder, out to fight the greed of big business and contributing to the intense hatred Pickens aroused at the companies he attacked.

George Keller, former chairman of Chevron

Thomas Boone Pickens Jr seemed destined for the oil industry from his birth in 1928. His father was an oil lease broker, and young T Boone went straight to Phillips Petroleum after graduating from Oklahoma State University with a degree in geology. By the age of 27 he had struck out on his own, first prospecting alone, then, in 1956, getting the $100,000 he needed to set up his first company.

It took a brief flurry of dealmaking in the early 1980s to focus national attention on Pickens, whose Mesa Petroleum had grown to become one of America’s biggest independent exploration companies. His genius was to spot the vulnerability of a group of companies far larger than his own, and find ways of exploiting their weakness for his own significant gain.

The oil price shocks of the 1970s were followed by falling demand and a glut of crude on world markets. That in turn left the shares of some of the biggest oil producers trading at less than half the value of their energy reserves.

Pickens later said he copied his idea from Dome Petroleum, a Canadian group that had launched a raid on Conoco. Selecting Gulf Oil as his target in late 1993, the oilman first assembled a stake in the company, then launched an offer to buy 15 per cent more, all the while agitating for Gulf’s directors to find ways to lift their company’s share price.

That led, within months, to a $13bn takeover of Gulf by Chevron, the biggest deal then undertaken. Pickens made $300m. Similar assaults on oil companies such as Unocal and his old employer, Phillips, did not yield such spectacular results. The Gulf deal, however, had already assured the oilman near-legendary status.

Pickens used a folksy popularism to cloak his financial acumen. The result was a disarmingly engaging manner that antagonised the corporate bosses who were the target of his raids.

America’s business leaders “are well off, and they all possess enormous egos”, Pickens wrote in his autobiography, published in 1987. “But they envy one another, constantly comparing the size of their companies and their executive perks,” he said.

Such comments had the expected effect. “He’s nothing but a pirate,” an executive at his first target, Cities Services, once said. George Keller, chairman of Chevron, voiced another widely held feeling: “Pickens does not break any laws doing what he does. But he breaks tradition.”

To Pickens, corporate executives such as these were “bureaucrats, caretakers. They have learned to move up through the bureaucracy with a minimum of personal risk. It’s a special talent.” He argued that such people should own large stakes in their own companies to make them more attuned to their shareholders — a view that, within a decade, had become standard management thinking.

Throughout it all, the raider from the Texas Panhandle preached the virtues of hard work and physical fitness. A basketball player in his youth, Pickens continued to play racquet games through most of his life, and was a fan of the company gym. “Physically fit employees are more alert, more productive and more creative, and they exhibit more team spirit,” he once said.

Perhaps fittingly, it took a spectacularly unsuccessful bet to put an end to Pickens’ career as a raider. Though successful at finding undervalued oil reserves on the stock market, he had proved fallible before at finding reserves under the ground: Pickens once said that it was a looming $400m-500m loss in his exploration business that prompted the attack on Gulf in the first place.

By the early 1990s, a big investment in a natural gasfield in the US had turned sour as prices failed to rise as Pickens had expected. A former Mesa lieutenant, David Bachelder, joined forces with hostile shareholders to force Pickens on the defensive: at the end it was the old raider who was portrayed as the enemy of shareholder value, a fat cat clinging desperately to corporate power. At the age of 68, there was little left but to surrender the company to a friendly investor group and bow out quietly.

Pickens remained in the limelight after leaving Mesa. In 2008, as crude oil prices were hurtling towards a record $145 a barrel, he undertook a $100m campaign to convert the US car fleet to natural gas and develop other domestic sources of energy such as wind. The “Pickens Plan” failed to revolutionise Detroit, though gas and renewable energy production have since soared in the US.

He also ran BP Capital, the energy-focused hedge fund he founded in 1996, and was known for big bets. Confidential data released by US senator Bernie Sanders revealed Pickens’ positions in natural gas futures rivalled those of Wall Street banks and big energy producers.

Gary Ross, an energy analyst who advised Pickens for large parts of his career and whose son once worked for BP Capital, said that at one stage in 2008 his fund was up as much as $4bn on its positions as oil and gas prices exploded.

“The banks just gave him everything he wanted, and he was able to make a fortune; it was just unbelievable,” Mr Ross told the Financial Times earlier this year.

In 2017 Pickens divorced his fifth wife, Toni Brinker, and put his 65,000-acre ranch in Texas up for sale for $250m. Last year he closed down BP Capital, citing ill health. He is survived by five children and 11 grandchildren.

Additional reporting by Gregory Meyer in New York and David Sheppard in