The accent might be the strangest part of all, for it bears no relation to his native Bristol dialect. To the American ear, it registers as London, and to the English ear, it registers as nowhere at all. “Mid-Atlantic” is the usual catchall. But one of the lessons of Scott Eyman’s estimable and empathetic biography, “Cary Grant: A Brilliant Disguise,” is that the accent was built in the same way as the speaker: from bits and pieces collected here and there.

The childhood was working-class Hobbesian. Multiple addresses. Days and nights without food or clothing. A roving, alcoholic father and a mother unsettled enough, according to prevailing Edwardian standards, to be committed to an asylum. Young Archie Leach was told that she was dead (and wouldn’t learn otherwise until he was already a movie star).

He escaped by joining a traveling acrobats’ troupe and following it to America. Desperate for money, he sold neckties on the streets of New York, walked on stilts at Coney Island for five bucks and five hot dogs a day. At one vaudeville engagement, he shared a bill with a water nymph, four performing seals and “The Eminent Girl Saxophonist.” By dint of persistence and handsomeness, he found work as a 1920s Broadway male ingenue, but even when Hollywood came calling, he showed no signs of exorbitant talent. He might have gone down in movie history as Mae West’s rather stiff and distracted love interest had he not been mysteriously unleashed by a string of late-1930s screwball comedies.

With “Topper,” “The Awful Truth,” and “Bringing Up Baby,” the recently christened Cary Grant found his truest expression as farceur: virile and subtle, intelligent and flummoxed and — crucially — not quite believing in his own attractiveness. As Pauline Kael wrote in her superb essay “The Man from Dream City” that combination of animal energy and diffidence made Grant “the most publicly seduced male the world has known.” Actresses chased him from one end of the screen to the other, and for the next three decades, working with directors as divergent as George Cukor, Howard Hawks and Alfred Hitchcock, he adapted his tightly honed, self-invented persona to the demands of every genre that would have him.

His reward was to become, until his retirement in 1966, the rare star whose star never wavered.

Even at today’s remove, it can be extraordinary to revisit a movie like “Notorious” or “The Philadelphia Story” or “North by Northwest” and find an actor whose work has not aged a second — has only deepened. In one brilliantly swift sequence in “His Girl Friday,” his shyster newspaper editor deceives a not-very-sharp rival (played by Ralph Bellamy), then watches as the deception is revealed, then expresses amazement that the rival ever fell for it. It all passes like the fluttering of moth’s wings, and there is no forgetting it.

Grant’s co-stars testified to his hard work, his concentration, his preparation. Eyman rightly homes in on his inner chiaroscuro, that never-resolving oscillation between dark and light — or, if you like, between Archie Leach and the man he became. Refracted through a camera lens, that struggle cohered into something like magic; in real life, it dissolved into its two combatants.

One of them, you might say, was Hollywood’s most notorious tightwad, staving off the terror of poverty by stiffing servants and handing houseguests itemized bills. The other subsidized his good friend, playwright-director Clifford Odets, until the end of Odets’ days. One was an anxiety-ridden basket case who drove four wives to distraction and became no more manageable after a hundred-plus LSD sessions. (As a proselyte, he was second only to Timothy Leary.) The other doted on children and rained down decades’ worth of deferred love on his late-in-life daughter.

The duality was perhaps most pronounced when it came to Grant’s sex life. Gossip had dogged him from his earliest days in Hollywood when he was photographed splashing around with housemate Randolph Scott, and for today’s LGBT community, it has become an article of faith that he was “one of us.” Yet the many women in his life testified to an ardent lover. “Why would I believe that Cary was homosexual,” asked third wife Betsy Drake, “when we were busy” fornicating? Eyman, treading as carefully as a bomb-disposal team, declares, “There is plausible evidence to place him inside any sexual box you want — gay, bi, straight, or any combination that might be expected from a solitary street kid with a street kid’s sense of expedience.”

Mealy-mouthed? Or just the resigned sigh of a biographer who can no more get a handle on his subject than his subject could? “You don’t look like Cary Grant,” someone once told him. “I know,” he said. “Nobody does.”

Louis Bayard is a novelist and reviewer whose most recent book is “Courting Mr. Lincoln.”

Cary Grant

A Brilliant Disguise

By Scott Eyman

Simon & Schuster. 304 pp. $35