GEOFF BENNETT: For decades, Roy Cohn operated at the at the center of American power, from his work with Senator Joseph McCarthy to his role as a lawyer, political fixer, and mentor to a young Donald Trump.

Now a leading biographer traces Cohn's life and the influence he still exerts on American politics 40 years after his death.

Our senior arts correspondent, Jeffrey Brown, has the story for our arts and culture series, Canvas.

KAI BIRD, Author: He was a villain flat out, I mean, without any question, but an interesting villain.

JEFFREY BROWN: He is Roy Cohn, one of the most polarizing figures in 20th century American life.

His new biographer is Kai Bird, who heads a center on biography at the CUNY Graduate Center in New York.

KAI BIRD: You know, the biographer doesn't have to like or admire your subject.

You just have to be obsessed and figure out what makes this villain tick.

JEFFREY BROWN: Bird is best known as co-author of the Pulitzer Prize-winning "American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer."

CILLIAN MURPHY, Actor: What do you know about quantum mechanics?

JEFFREY BROWN: The basis for the Oscar-winning 2023 film.

And many of his books have centered on leading establishment figures of the postwar era, most recently a biography of Jimmy Carter.

In his latest, "American Scoundrel," written with Susan Goldmark, his wife and chief researcher, he found something different.

KAI BIRD: It suddenly occurred to me that I'd spent all these decades writing about these powerful establishment figures.

And that world was gone.

It disappeared.

There's no longer this bipartisan consensus in our political world.

And there's instead this divisive world that was created by Roy Cohn.

JEFFREY BROWN: He was more important than you would ever imagine.

KAI BIRD: Yes, suddenly in - - over the last 10 years, because of the Trump era, he suddenly is clearly haunting us from his grave.

MAN: Judge Kaufman pronounced the death sentence.

JEFFREY BROWN: In the 1950s, Cohn, still in his twenties, burst into the national spotlight as prosecutor in the espionage trial that led to the execution of Julius and Ethel Rosenberg.

ROY COHN, Attorney: Roy Cohn is here speaking for Roy Cohn to give the facts.

JEFFREY BROWN: And as chief counsel to Senator Joseph McCarthy in his anti-communist crusade.

KAI BIRD: He was the attack dog that Joe McCarthy sent out.

And Joe McCarthy was sort of an empty vessel.

JEFFREY BROWN: What jumped out at you?

What stood out especially vis-a-vis Roy Cohn's involvement?

KAI BIRD: Roy was a gay, closeted man then, but he went after gay civil servants in the State Department ruthlessly.

He knew exactly what he was doing.

He had this private life, and yet he was shamelessly going after fellow gays.

That was shocking.

JEFFREY BROWN: In Bird's telling, Cohn was fueled by ambition and resentments, ruthless with perceived enemies, pushing up to and beyond legal boundaries for friends, with an attention-getting personal style and flamboyance.

KAI BIRD: I quote in the book H.L.

Mencken's observation that the world would be a very dull place for us honest men if it were not for the sinners.

And that's Roy Cohn.

He was fascinating.

He was charming over the dinner table.

But he was transactional.

JEFFREY BROWN: So he knew how to make things happen.

KAI BIRD: He knew how to make things happen to fix things for people.

JEFFREY BROWN: In New York, his clients included mafia heads and the owners of Studio 54, the famed nightclub at the heart of '70s celebrity life, of which Cohn himself was a fixture.

He made and helped friends in high places, including mentoring a then-27-year-old developer named Donald Trump.

KAI BIRD: Trump had an annoying federal case that was being filed by the Fed's against some of his housing developments in Queens, accusing the Trump Organization of anti -- discrimination against Blacks.

And Roy's advice to him was, don't settle.

JEFFREY BROWN: Fight.

KAI BIRD: Fight, fight, attack, counterattack.

In fact, sue them for libel, which was outrageous.

This was the kind of advice that the young Trump relished.

He became essential to the rise of the young Trump.

JEFFREY BROWN: The two would remain close personally and professionally for years.

And, decades later, in his first term, angry at then Attorney General Jeff Sessions for recusing himself in the probe of Russian election interference, Trump reportedly demanded, "Where's my Roy Cohn?"

KAI BIRD: He was under indictment at that point by Robert Morgenthau for bribery.

JEFFREY BROWN: Bird showed us FBI investigation files.

Cohn was indicted three times, including for perjury, bribery, and extortion.

Remarkably, he beat every charge, though he was eventually disbarred for professional misconduct shortly before his death in 1986 at age 59 from complications related to AIDS.

AL PACINO, Actor: I'm going to be a lawyer, Joe.

JEFFREY BROWN: In his afterlife, he's been played by Al Pacino in the TV series based on Tony Kushner's Pulitzer-winning play "Angels in America."

JEREMY STRONG, Actor: I'm brutal.

That's right.

JEFFREY BROWN: More recently by Jeremy Strong opposite Sebastian Stan's young Donald Trump in the film "The Apprentice."

But his most enduring afterlife, says Kai Bird: KAI BIRD: It's his values, his resentment of the establishment that now prevails in our politics.

He is the architect of this politics of resentment, resentment against the establishment, of the elites, this sort of right-wing populism, this suspicion of immigrants.

This is all Roy Cohn.

JEFFREY BROWN: You have to live with this person for a long time, a person you have described as a bad person.

How do you do it?

KAI BIRD: Gleefully.

JEFFREY BROWN: Really?

KAI BIRD: I had no problem sleeping at night.

As the biographer, you're -- you want to become obsessed, and I was.

JEFFREY BROWN: All right.

The book is "American Scoundrel."

Kai Bird, thank you very much.

KAI BIRD: Thank you, Geoff.