In October of 1975, dining in Rome, Gore Vidal told his new friend the novelist Michael Mewshaw that Françoise Sagan was “a magnum of pure ether.” He didn’t stop to clarify, but rigor was beside the point; the Vidalian bon mot was about the speaker, not about the subject. In the course of more than half a century, his quips, aphorisms, insults, and punch lines amounted to a self-portrait, airbrushed so as to highlight his favorite warts: Olympian detachment, patrician hauteur.

It was an act, a put-on—perhaps the most effective double bluff in the history of literary P.R. In 1977, after visiting Vidal at his cliff-perched villa on the Amalfi Coast, Martin Amis observed that “he has little of the paranoia worryingly frequent among well-known writers.” Norman Mailer had been onto something, Amis concluded, when he said that “Vidal lacks the wound.”

“My God,” Vidal told Amis, “what a lucky life.” The official story, as set down in Vidal’s memoirs and essays, and in hundreds of reviews, profiles, and, finally, in his obituaries—he died in 2012—went like this: grandson of Thomas P. Gore, the blind senator from Oklahoma, son of Gene Vidal, a high-school football star whose exploits as an aviation pioneer landed him on the cover of Time, he was born in 1925, at West Point, grew up in Washington, D.C., and studied at Exeter. If asked about his mother, Nina Gore, who had swapped family life for a succession of boyfriends and husbands, Vidal would explain that her desertion—and her alcoholism, and her sexual confessions—hadn’t really bothered him. (A reporter bold enough to press the subject would be silenced with a reference to Freudian quackery.)

At seventeen, Vidal would explain, he “quit schooling” for good and enlisted in the Army, served as first mate on a supply ship in the Aleutian Islands, and then—almost by accident, virtually without sweat, and for the simple reason that he could—became a novelist (“Julian,” “Myra Breckinridge,” “Burr,” “Creation”), essayist (“Homage to Daniel Shays,” “The Hacks of Academe”), playwright (“Visit to a Small Planet,” “The Best Man”), screenwriter (“Ben-Hur”), politician (valiant failed campaigns for Congress, in New York, and for the Senate, in California), actor (“Bob Roberts,” “Gattaca,” “Igby Goes Down”), steel-chinned prime-time brawler (points victories over Buckley in 1968 and Mailer in 1971), and friend to everyone worth knowing (Greta, Tennessee, Eleanor, Orson, Mick, Sting). Yet he remained immune to the seductions of celebrity and clear-eyed about the workings of power. Stepbrother of a sort to Jacqueline Bouvier, he had been a welcome guest at Hyannis Port and the White House until he grew bored with the whole thing and unmasked Bobby Kennedy (notable for his “vindictiveness” and “simple-mindedness about human motives”) in his essay “The Best Man, 1968” and then the Kennedy courtiers in “The Holy Family” and “The Manchester Book.” Later efforts in this truth-to-power vein had titles like “Shredding the Bill of Rights,” “State of the Union, 1975” (it wasn’t good), “State of the Union, 1980” (worse), and “State of the Union, 2004” (don’t ask).

And while his contemporaries—as speared in his essay “American Plastic: The Matter of Fiction”—nervously tracked their positions on the New York literary stock exchange, Vidal lived in regal exile with his partner, Howard Austen, quite impervious to what anyone thought about his writing, his quoted comments, or his sexual proclivities. The one sign of human frailty was his insistence that the hordes of visiting photographers favor his “good” side, the left.

This was the figure known to most, but not to all. At the end of the war, Warrant Officer Vidal was stationed at Mitchel Field, on Long Island, and working part time for the publisher E. P. Dutton. He came into the city whenever he could. On a Sunday in November of 1945, he attended a lecture on love at the Ninety-second Street Y. It was here that he met Anaïs Nin.

Born in France to Cuban parents, Nin, who was forty-two, was writing fiction alongside a diary that she would one day publish. “He has great assurance in the world, talks easily, is a public figure, shines,” Nin wrote, after Vidal paid a visit to her studio. “He can do clever take-offs, imitate public figures.” He is also “lonely,” “hypersensitive,” “insecure.” When Vidal opened up to her—“He dropped his armor, his defenses”—it was not to talk about his grandfather the senator or his father the aviator but his mother the deserter. “Psychologically,” Nin wrote, “he knows the meaning of his mother abandoning him when he was ten, to remarry and have other children.”

At first, Vidal was thrilled by the connection. Returning from a trip to Washington, D.C., he told her, “You have cast a spell on me. What I once accepted, I now do not like. I found my grandfather, the senator, boring.” But the spell soon wore off. In March of 1946, Vidal invited Nin to a dinner at the PEN Club. “Was shocked by the mediocrity of the talks,” she wrote. “A ‘literary’ world so thoroughly political, intriguing, and commercial, but a world Gore intends to conquer.” The next month, she writes, “Gore in the world is another Gore. He is insatiable for power. He needs to conquer, to shine, to dominate.” In November, she notes that Vidal’s letters—he had then retreated to write in a Guatemalan monastery that he had acquired for a pittance—“sound attenuated, diminished, dulled. Lack of faith, of responsiveness to surroundings and people. A blight.” By December, she admits defeat: “Whatever Gore was with me, whatever side he showed me, was not the one he was to show in his life and in his work.”

“The Diary of Anaïs Nin, Volume Four: 1944-1947” was published in 1971, and Nin’s use of the past tense carries a hint of retrospect, as if she were taking account of later developments. In 1970, the composer Ned Rorem, another diarist friend, described the “cynical stance” that Vidal had perfected over the previous quarter century: “Those steely epigrams summing up all subjects resemble the bars of a cage through which he peers defensively. ‘It’s not that love’s a farce—it doesn’t exist.’ . . . Rather than risk being called a softy, he affects a pose of weariness.”

Jay Parini, in his authorized biography, “Empire of Self: A Life of Gore Vidal” (Doubleday), wants to give us the real Gore, but he keeps on falling for the pose. Although Parini exhibits some skepticism toward his subject, and notices that Vidal’s claim of indifference to the world’s opinion was at odds with the many framed magazine covers and threats of libel suits, he begins each chapter with an epigraph culled from Vidal’s table talk and publicity spiel. When it comes to telling the story of the life, Parini proves content to deliver the strapping, self-assured, untouchable Vidal, the builder and overseer of a well-protected, many-colonied “empire of self”—a phrase repeated throughout the book, in a dizzying range of connections.

As Parini approaches Vidal’s later years, his defensive instincts go into overdrive. He praises an essay on John Updike—ten thousand words of ill-argued bile—as “a kind of cultural service,” and declares Vidal “more relevant than ever” in the years after 9/11, when he was in the habit of writing things like: “The unlovely Osama was chosen on aesthetic grounds to be the frightening logo for our long-contemplated invasion and conquest of Afghanistan.”