In 1972, on the 10th anniversary of Marilyn Monroe’s death, Gloria Steinem wrote an essay for Ms. magazine titled “The Woman Who Died Too Soon.” As a teenager, Steinem had relished the celluloid darkness of the matinee: the sci-fi flicks, the serials, the stubborn charm of Doris Day. She loved them all, however improbable the plots or poor the acting. But she walked out of “Gentlemen Prefer Blondes.” The sight of Marilyn as the diamond-obsessed showgirl Lorelei Lee, “huge as a colossus doll, mincing and whispering and simply hoping her way into total vulnerability,” enraged her.

Lorelei’s doe-eyed desire for approval felt dangerous to Steinem — an affirmation of the power of the male gaze. But she would come to see, in the star’s own sadness, in her winking innocence and complex sexuality, a woman straddling the puritanism of postwar America and its dissolution in the ’60s. Marilyn died, at 36, on the eve of the publication of “The Feminine Mystique” and the rise of second-wave feminism. What if she had lived? Who would she — who could she — have become? “When the past dies there is mourning,” Steinem later wrote, “but when the future dies, our imaginations are compelled to carry it on.”

It has been 50 years to the day since Marilyn died. There have been countless biographies, novels, plays (including Arthur Miller’s “After the Fall,” with its grotesque caricature), conspiracy-oriented chronicles of her final days, and her own ghostwritten autobiography, published posthumously. There have been almost as many versions of Marilyn: she was brazenly sexual, shy and insecure, a dumb blonde and a bookworm who read Dostoyevsky; she was gentle and free-­spirited, spiteful and cannily controlling; she could barely act, vamping for the camera, or she was a brilliant comedian, playing a pinup version of Shakespeare’s fool.

Nobody is one thing all the time. Yet Marilyn is steeped in paradoxes so profound that, even under the microscope, they stir and shift without ever settling into a singular picture. Such is the premise of Lois Banner’s new biography, “Marilyn: The Passion and the Paradox,” which behaves a little like its subject. Weaving together exclusive interviews, material from previous books and, most significantly, the contents of Monroe’s two long-lost personal filing cabinets (made available to the public only last year, when Banner published a selection from them in “MM — Personal”), Banner presents a rich and often imaginative narrative of Marilyn’s life. By the end, Monroe feels at once like an earthly being — an almost-friend — and an enigma, still slightly out of focus and just beyond reach. That seems right.