‘Donald calls me 15 to 20 times a day,” Roy Cohn told me on the day we met. “He is always asking, ‘What is the status of this . . . and that?’ ”

It was 1980. I had been assigned to write a story on Donald Trump, the brash young developer who was then trying to make a name for himself in New York City, and I had come to see the man who, at the time, was in many ways Trump’s alter ego: the wily, menacing lawyer who had gained national renown, and enmity, for his ravenous anti-Communist grandstanding.

Trump was 34 and using the connections of his father, Brooklyn and Queens real-estate developer Fred Trump, as he navigated the rough-and-tumble world of political bosses. He had recently opened the Grand Hyatt Hotel, bringing life back to a dreary area near Grand Central Terminal during a period when the city had yet to fully recover from near bankruptcy. His wife, Ivana, led me through the construction site in a white wool Thierry Mugler jumpsuit. “When will it be finished? When?,” she shouted at workers as she clicked through in stiletto heels.

The tabloids couldn’t get enough of the Trumps’ theatrics. And as Donald Trump’s Hyatt rose, so too did the hidden hand of his attorney Roy Cohn, always there to help with the shady tax abatements, the zoning variances, the sweetheart deals, and the threats to those who might stand in the project’s way.

Cohn was best known as a ruthless prosecutor. During the Red Scare of the 1950s, he and Wisconsin senator Joe McCarthy, the fabulist and virulent nationalist crusader, had hauled dozens of alleged “Communist sympathizers” before a Senate panel. Earlier, the House Un-American Activities Committee had skewered artists and entertainers on similar charges, resulting in a trail of fear, prison sentences, and ruined careers for hundreds, many of whom had found common cause in fighting Fascism. But in the decades since, Cohn had become the premier practitioner of hardball deal-making in New York, having mastered the arcane rules of the city’s Favor Bank (the local cabal of interconnected influence peddlers) and its magical ability to provide inside fixes for its machers and rogues.

“You knew when you were in Cohn’s presence you were in the presence of pure evil,” said lawyer Victor A. Kovner, who had known him for years. Cohn’s power derived largely from his ability to scare potential adversaries with hollow threats and spurious lawsuits. And the fee he demanded for his services? Ironclad loyalty.

Trump—who would remain loyal to Cohn for many years—would be one of the last and most enduring beneficiaries of Cohn’s power. But as Trump would confide in 1980, he already seemed to be trying to distance himself from Cohn’s inevitable taint: “All I can tell you is he’s been vicious to others in his protection of me,” Trump told me, as if to wave away a stench. “He’s a genius. He’s a lousy lawyer, but he’s a genius.”

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Bleak House

On the day I arrived at Cohn’s office, in his imposing limestone town house on East 68th Street, his Rolls-Royce was parked outside. But all elegance stopped at the front door. It was a fetid place, a shambles of dusty bedrooms and office warrens where young male assistants made their way up and down the stairs. Cohn often greeted visitors in a robe. On occasion, I.R.S. agents were said to sit in the hallway and, knowing Cohn’s reputation as a deadbeat, were there to intercept any envelopes with money.