In January 2000, the New York Times received one of Norman Mailer’s frequent and furious letters to the editor, this time complaining about factual errors in a recent Mailer biography. “It may be healthier to read no biography about yourself until you are turning in the grave,” Mailer concluded.

Nearly six years after the author’s death, a biography arrives to which Mailer himself might again respond ferociously—this, despite the volume in question being the authorized biography to which Mailer contributed hundreds of interviews, access to his personal archives and more than 45,000 letters written over the course of a lifetime. At 960 pages, Norman Mailer: A Double Life is a behemoth of appropriate scope to frame a man who led a big life and produced masterpieces like The Naked and the Dead and The Executioner’s Song.

“Biographies, in my view, are always approximations of a life,” J. Michael Lennon, Mailer’s longtime friend and official biographer, explains. “I know it wouldn’t please him entirely. He’d say, ‘You got the nuance wrong here,’ or ‘You mixed people up.’ I know from working on his letters with him that he was good at remembering and making factual corrections. He was also a biographer himself, so he understood the craft. He was very speculative about the people he wrote about and used his own personality as a kind of divining rod for the people that intrigued him.”

In fact, Lennon held many roles in the life of Norman Mailer and continues to hold them today. After writing his dissertation on Mailer’s 1968 novel, The Armies of the Night, Lennon tracked the author down at a book signing in 1971, after which the new friends closed down the local bar. Lennon worked alongside Mailer for decades, collaborating with him on later books and becoming his literary executor in 1981. Following the publication of his biography, Lennon will quietly return to the task of editing and publishing a critical sampling of Mailer’s massive collection of letters.

“Mailer knew me as an archivist and a bibliographer and a fact fetishist who collected the bits of his life and work,” Lennon says. “At some point, I told myself, this is the work of your lifetime. You’re never going to do anything more important than this. So, for seven years, I worked on it every day. I really tried to bring in material that no one had ever seen before, and God knows I had plenty of it. I have the letters and all my interviews with him and all the interviews with his family. Those are three things that no other biographer has access to, so I was a lucky guy.”

Lennon also credits the work of Mailer’s first biographer, Robert Lucid, who died in 2006, leaving Lennon to inherit the great work, as well as longtime Mailer collaborator Lawrence Schiller for their contributions to the biography. As to the significance of the subtitle, A Double Life, Lennon says at some point it just seemed to fit the best.

“It’s been used many times to describe him, but it’s not just that there are these two enclaves to his life,” he says. “Every identity that he had—and he had dozens of identities, occupations and avatars, whether he was playing author, playwright, politician or raconteur—always had another half to it….I think part of it was because he was always interested in ‘The Other,’ the minority of good in evil people and the minority of evil in good people. He was always looking for that minority that would help define and give personality to other people.”

Lennon also explains how Mailer was really a writer born into two generations: the post–World War II writers in the vein of James Jones and the 1960s movement that evolved into New Journalism.

“The writers who came out of World War II realized that a great generation of writers had emerged from World War I,” says Lennon, a professor emeritus of English. “You’re talking Hemingway, Dos Passos, Fitzgerald, Faulkner. Mailer saw that this was the chance to enter that second wave, following an even bigger war.”

Lennon learned much about his friend after reading nearly 50,000 of his letters. Lennon helped broker the 2005 sale of nearly 1,000 boxes of archival material to the Harry Ransom Center at the University of Texas at Austin, where it remains the library’s largest single author archive.

“I learned the depth of his depression in the 1950s,” he says. “After publishing three novels, he was ready to quit writing by 1956. Those were the worst years of his life. He kind of wrote himself out of that period with Advertisements for Myself, but he continued to experience struggles with his art, his wives, his children.”

Asked if Mailer was taken aback with his reputation as a womanizer, Lennon speaks the truth. “It’s hard to avoid the label,” he says. “He had dozens of affairs, but most of them were ones where he stayed involved with those people because he liked them. No one loved women more than he did. And he told me to be candid about his relationships. He said, ‘Analyze it, take it apart. If you are ever in doubt about my motivation in a given situation, cherchez la femme: There’s a woman at the bottom of it.’ There’s a lot of truth in that statement.”

For someone who was that close to a titan of American literature for more than 35 years, Lennon has been admirably reticent to trade on that relationship. Even when speaking at Mailer’s memorial at Carnegie Hall in 2008, Lennon would only speak about Mailer the writer, not Mailer the man.

“Maybe down the line,” he says. “The important thing was to get a good biography out there that gets the timeline right and puts the major accomplishments down. These are the formal things that need to be done to establish his position in the canon and in American life.”

At the same time, he remembers joyful evenings spent at the Mailer kitchen table and storytelling in bars and late-night poker sessions. “We were buddies,” Lennon says.

In later years, Lennon would become a constant in Mailer’s life, flying with him to speaking engagements and showing up at Mailer’s house, where he was welcomed as an honorary member of the family. In this definitive biography, he feels he has left no stone unturned. “The idea of being Norman Mailer’s Boswell was never far from my mind.”

Clayton Moore is a freelance writer, journalist, book critic and prolific interviewer of other writers. His work appears in numerous newspapers, magazines and websites. He is based in Boulder, Colorado.