Almost a decade ago, when I began research for my biography of Elinor Glyn (1866–1943), the notorious redheaded British sex novelist turned early-Hollywood doyenne, I came across a photo from 1930 of photographer Sir Cecil Beaton dressed as Glyn. Two generations younger than the woman he impersonated, Beaton captured Glyn as a modern siren.

When I first saw the photo, I knew Glyn only from writing my first book, Go West, Young Woman! The Rise of Early Hollywood, which touched upon her last, great act as a scriptwriter during the Roaring 20s. But given Beaton’s status as perhaps the 20th century’s sharpest eye, the image clinched her status as the It Girl whose style shaped so many others to come. Indeed, she was the founding mother of all her era’s It Girls. Hollywood stars such as Gloria Swanson and Clara Bow boldly inhabited the love scenes she wrote in her novels, which were later adapted into movies.

Glyn’s final act took place during Prohibition, when she reigned as the impossibly elegant and eccentric screenwriter whom colleagues such as Samuel Goldwyn, co-founder of Paramount Pictures, and director Cecil B. DeMille credited with the “paradox of bringing good taste and sex appeal” to Hollywood, as Beaton once put it. Rose petals strewn across beds, silk negligées, kisses that travel from the palm to neck, and caresses with a hint of force were all her stock and trade.

Madame Glyn—the title she insisted on when she moved from England to Los Angeles in the early 1900s—used her aristocratic credentials, European savoir faire, and upper-class accent to still attacks from moralists and nativists concerned about un-American, immoral influences on Hollywood. (Plus ça change, plus c’est la même chose …) As Gloria Swanson, who often made the rounds with Glyn in the 1920s, recalled, “Her British dignity was devastating, as she baby-stepped through this or that dining room or garden party, people moved aside for her as if she was a sorceress on fire.”

Cecil Beaton impersonating Elinor Glyn at a party hosted by Elsa Maxwell, 1930.

Glyn taught the screen’s first seductresses and Don Juans how to walk, talk, dress, make love, and, most critically, manage the spotlight that had fallen on them by imitating her glamorous ideas. Her earliest protégés included Swanson, Bow, the great “Latin lover” Rudolph Valentino, and John Gilbert, whom Glyn dubbed the “Black Stallion,” much to his chagrin (all of whom feature in Damien Chazelle’s forthcoming Babylon, starring Margot Robbie, Brad Pitt, and Jean Smart as Elinor Glyn).

I certainly knew Glyn was a force. But the silvery print of Beaton—equal parts camp and realism—crystallized how she set the style for the day’s femmes fatales. By the time Beaton posed as Glyn, he was already a well-known Vogue photographer and portraitist. The occasion for his impersonation was a birthday party thrown by Elsa Maxwell—the 1950s gossip columnist known for hosting lavish parties. Maxwell had asked her friends to come as someone well known in Parisian society and even hired George Hoyningen-Huene, another Vogue photographer, to memorialize her often famous guests’ impressions of other famous folk.

Elinor Glyn is credited with the “paradox of bringing good taste and sex appeal” to Hollywood.

The photo of Beaton captured the signature features of Glyn’s romantic style, which became the hallmark of 1920s Hollywood films. Beaton dressed as the siren in all her glory: the silk-velvet sheath dress she favored in her later years, an impossibly long strand of pearls, and an elaborately braided cap of hair. He leaned against her signature décor, a tiger-skin rug that pairs comfort with animal instincts. (Glyn had a lifelong affinity for cats of all kinds.)

Beaton’s crucial prop was the cross, which dangled at the end of the pearls. At once tenderly held and coyly proffered, the cross adds the humorously transgressive umph that came to be associated with the witty woman who spearheaded the sexual liberation of Hollywood. Here was a picture demonstrating the irresistible legacy of Hollywood’s first influencer—who re-invented how to act like a woman, draped in a new imagery of sexually alluring femininity, while evoking the daring and freedom of a man.

Hilary A. Hallet is the Mendelson Family Professor and director of American studies and associate professor of history at Columbia University. Her book Inventing the It Girl: How Elinor Glyn Created the Modern Romance and Conquered Early Hollywood is out now from Liveright