One day in August, 2016, the financier Carl Icahn made an urgent phone call to the Environmental Protection Agency. Icahn is one of the richest men on Wall Street, and he has thrived, in no small measure, because of a capacity to intimidate. A Texas-based oil refiner in which he had a major stake was losing money because of an obscure environmental rule that Icahn regarded as unduly onerous. Icahn is a voluble critic of any government regulation that constrains his companies. So he wanted to speak with the person in charge of enforcing the policy: a senior official at the E.P.A. named Janet McCabe.

Icahn works from a suite of offices, atop the General Motors Building, in midtown, that are decorated in the oak-and-leather fashion of a tycoon’s lair in a nineteen-eighties film. During that decade, Icahn made his reputation as one of the original corporate raiders, pioneering the art of the hostile takeover and establishing himself as a human juggernaut—a pugnacious deal machine, all avarice and swagger. By the time he called the E.P.A., he was eighty, and long since unburdened of any personal or dynastic need to make money; according to Forbes, he is worth approximately seventeen billion dollars. Plenty of titans who are not as old and not as rich as Icahn have opted to devote their remaining years to spending their money, or to giving it away. Not Icahn. A tall man with a shambling manner, he recently grew a white beard, which softens his round face, giving him the cuddly appearance of an elderly Muppet. But he has not lost his taste for the kill. A few years ago, he sold his mega-yacht, because cruising on it bored him. He has engaged in philanthropy, building charter schools and a stadium on Randall’s Island that bears his name. But the charity circuit is a snooze. What Icahn loves beyond all else is to rise late each morning, and then to spend the rest of the day and much of the night working the phone, making deals. Years ago, a reporter asked Icahn why he kept making money when he already had more than he could ever spend. “It’s a way of keeping score,” he said. He is one of the wealthiest individuals not just in the world but in the history of the world—a man who takes pride in many things, not the least of which is his ability to get just about anybody on the phone.

“She’s on vacation,” McCabe’s assistant said, flatly.

For how long?

Two weeks.

To Icahn, there was something that simply did not compute about going on vacation and leaving one’s work behind. Surely, he insisted, McCabe could interrupt whatever leisure activity she was engaged in to take a pressing phone call from Carl Icahn?

No, McCabe’s assistant informed him. She couldn’t.

The old conundrum about whether it is better to be loved or feared has never posed much of a dilemma for Icahn. In “King Icahn,” a 1993 biography, the author, Mark Stevens, described his subject as a “germophobic, detached, relatively loveless man,” and quoted one contemporary saying, “Carl’s dream in life is to have the only fire truck in town. Then when your house is in flames, he can hold you up for every penny you have.” When the biography was published, Icahn stocked his office with copies to give to visitors. These days, he bristles at the term “corporate raider,” favoring the euphemism “activist investor,” but the reality is that when Icahn targets a company the response from management is generally terror. He has a volatile temper and a vindictive streak. Everyone makes time to take his calls.

Incredulous that Janet McCabe might not do so, Icahn asked, “What if the world’s falling apart?”

The refiner that he was worried about is CVR Energy, which is based in Sugar Land, Texas. In 2012, Icahn acquired a controlling stake in the company, with the intention of making it more profitable and then selling it at a higher price. But under the Renewable Fuel Standard—a law passed, under George W. Bush, to promote the use of ethanol and other biofuels—refiners like CVR are forced either to blend ethanol into their products or to purchase credits, known as Renewable Identification Numbers, from refiners that do. CVR did not make sufficient investments to blend ethanol into all its products, choosing to buy credits instead. When Icahn bought his shares in the refiner, RINs were cheap—about a nickel each—so it was reasonably affordable for the company to comply with the law. But in 2013 the price of RINs, which had been stable, began fluctuating, and by 2016 the company was spending two hundred million dollars a year on credits. When Icahn called McCabe, CVR’s stock had dropped seventy per cent from the previous year. This incensed him.

“Look, I’m too old to be politically correct,” he told CNBC, on September 13th. “This woman, Janet McCabe . . . she’s never run a business.” Icahn pointed out that, “at the risk of being immodest,” he had made a great deal of money in his career. “The government shouldn’t run things, because they aren’t trained to run things,” he continued. This is a core element of Icahn’s philosophy. Jimmy Williams, a former in-house lobbyist for Icahn, told me, “Carl is a man who thinks that business should be unfettered and that government should not be involved in the free-market economy. With every fibre in his body, that is what he truly believes.”

When Icahn couldn’t reach McCabe, he wrote a blistering open letter to the E.P.A., in which he demanded that the rules be changed so that other parties, and not refiners, would be responsible for blending ethanol or purchasing credits. “At the risk of being immodest,” he wrote, “most respected experts involved in markets and the way they function would agree there are few in the country that understand investing in markets better than I do.”

One person who was listening to Icahn was the Republican Presidential nominee, Donald Trump. Icahn and Trump have known each other for decades, and Icahn supported his friend’s aspirations for the White House at a time when they still looked quixotic. Trump has long boasted about his association with more successful businesspeople, dropping references to potentates the way kids decorate their school binders with the names of their favorite pop stars. But, in reality, many New York financiers considered him a buffoon. In 2015, Lloyd Blankfein, the C.E.O. of Goldman Sachs, greeted the suggestion that Trump might run for President by remarking that the notion of the former star of “The Apprentice” having his “finger on the button blows my mind.” In this context, an endorsement from Icahn was a precious credential. On the campaign trail, Trump bragged about his “very dear friend Carl Icahn,” the name functioning as a byword for boundless prosperity.

If Icahn was willing to be enlisted in this fashion, he was also prepared to drop Trump’s name when it served his interest. Appearing on Bloomberg TV on August 16, 2016, he vowed that Trump would put an end to “these crazy regulations” on his first day in office. In fact, Icahn continued, he had spoken with Trump about the E.P.A. rule obliging his refiner to purchase renewable-fuel credits. If elected, Trump “will stop that,” Icahn promised. “That’s a hundred per cent.”