In G-Man (Viking, Nov.), historian Gage examines how FBI director J. Edgar Hoover shaped, and was shaped by, the 20th century.

Among other aspects of Hoover’s early life, you highlight his membership in the Kappa Alpha fraternity at George Washington University.

When I sat down with the Kappa Alpha journal and realized it was this deeply Southern, Lost Cause fraternity, it really explained to me how Hoover conceived of himself and the FBI. The other pieces that surprised me were materials about his difficult family life, particularly his parents’ childhoods and upbringing, the deaths and the suicides and the bank failures and the murders. Hoover tended to describe his childhood as this idyllic experience, when he talked about it at all.

It’s shocking nowadays to read that at the height of Hoover’s campaign against Martin Luther King Jr. most Americans sided with the FBI director.

That’s what excites me as a historian—finding those moments that upend what we assume, not only about the present but about the ways the past fed into the present. One of the big themes of the book—and in some ways maybe the most surprising thing about it—is just how popular, influential, and widely revered Hoover was for most of his life. For the bulk of his career, for better or for worse, he was one of the most universally respected and popular figures in American history. That tells us something incredibly important, both about Hoover himself and our flattering narratives about who we are as a country.

What’s changed about the FBI director’s role since Hoover?

The director’s role in a formal sense has changed a great deal—it is a presidential appointment, it requires Senate approval, it’s time-limited at least in theory, and there are a lot more mechanisms of accountability. But there are some real ways in which Hoover’s institutional stamp is still there, including his sense of the FBI as an apolitical professional investigative force that is supposed to stand outside of all the political drama, and yet also has this cultural conservatism that Hoover put in place. Those two themes, the ideological conservatism and the professional government “progressive ethos”—Hoover put them together. The FBI is still an institution that is playing with those things.

You also explore Hoover’s “intimate relationship” with his second-in-command, Clyde Tolson. Am I right in understanding that Hoover’s idea of who an FBI man was—a clean-cut white man in a suit—was also his type in men?

His personal life, his sexual desires, all of those things that you’re reading between the lines, on the lines—I would certainly say that that’s true. He had a type of man that he admired and the boundaries between personal admiration and professional admiration were often quite blurry.