Of all the honors accorded Sonia Rykiel over the course of her long career (including France’s Legion of Honor and an “Oscar” from the Fashion Group International), perhaps none is more conspicuous than le Club Rykiel on the menu of the Café de Flore, renowned as the gathering place for the surrealists, the existentialists, assorted intellectuals, local residents, expatriates, and tourists. As befits a sandwich named for a sparrowlike fashion designer, this one has no bread. Until recently, Rykiel could be found most days at a table for four at the crook of the L-shaped room upstairs: a pale woman dressed in black, her eyes rimmed in kohl. Her trademark wedge of red hair has prompted Marek Halter, one of several novelists she counts among her friends, to note a certain resemblance to Hatshepsut, the female pharaoh.

Today, her table is occupied by Julie de Libran, the designer appointed last year to steer the company that bears Rykiel’s name. She’s taller than Rykiel, with lavish, tousled blonde hair, and she, too, is hard to miss—dressed in torn jeans, spike-heel boots, a black sweater, and carrying a black Birkin bag. Even before her current position was announced, de Libran, 42, who served for six years as Marc Jacobs’s right hand at Louis Vuitton, had emerged as a cult style icon, her every sartorial choice breathlessly dissected on countless blogs. You could airlift her into Los Angeles, Milan, New York, London, or any number of other cultural capitals, and she would look at ease and chic, as if she belonged. Trilingual, de Libran speaks English without an accent—or, rather, with an accent that is singular and unplaceable, marked by intermittently British-sounding vowels and occasional Italian-style rat-a-tat consonants. She is, in fact, the embodiment of a contemporary ideal—the globe-trotting citizen of the world—just as Rykiel was the embodiment of a popular ideal in her own time: the Left Bank Parisienne.

Residents of Saint-Germain-des-Près complain that their neighborhood has become a shopping mall, with fewer services and local businesses. In the single block of the Rue des Saints-Pères, where Rykiel lives and went to work every day for four decades, the pharmacy, the Irish pub, and the antiquaire selling chandeliers are gone, replaced by boutiques offering high-priced Italian handbags and the latest men’s wear. It was, in fact, Rykiel who planted the fashion flag, nearly a half-century ago, when her first shop opened its doors on the Rue de Grenelle in May 1968—and then temporarily had to close them while students took to the streets and workers went on strike in anti-establishment protests that paralyzed the country. The area then was best known as home to the Sorbonne and the Ecole des Beaux-Arts, to writers, artists, philosophers, musicians, and filmmakers, to jazz clubs, cellar bars, galleries, cinemas, and bookstores—but not to boutiques selling fashion. The stomping ground of the disaffected and the deeply cool, the Left Bank offered glamour of another variety: moody, bohemian, veiled by a Gauloise haze.

With no formal training, Rykiel got her start designing clothes she wanted to wear but couldn’t find, and selling them at Laura, the shop her husband, Sam, owned on the Avenue du Général Leclerc. In 1955, pregnant with her daughter, Nathalie, Rykiel devised a dress that flouted the convention of the time, when pregnant women camouflaged their bulging bellies. With its fitted bodice, flowing skirt, and flattering lines, it was soon in demand not only as maternity wear but even among women who weren’t pregnant. It was, however, Rykiel’s sweaters that solidified her reputation. Ribbed, with high armholes that made the shoulders seem small and the torso narrow, they hit at the hip bone, with a proportion that made the legs seem longer. They were an instant sensation; the English press dubbed them “poor-boy sweaters.” Audrey Hepburn bought an array, in a spectrum of colors.

From there, Rykiel branched out, creating the components of a wardrobe with what she called “clothes that have no shape unless they are worn.” Knits, without a bra underneath, followed the body. Jackets skimmed the torso. Culottes provided the silhouette of a skirt and the freedom of trousers. Marabou jackets delivered all the impact of fur but in soft, light, fluid shapes. Nathalie Rykiel, who grew up to work alongside her mother and eventually run the business, sums up the style as “sexy and comfortable—two words that had never been put together before.”

By the early ’70s, Rykiel had acquired an avid following in Paris and abroad, designing for a woman who was sensual, intelligent, and sexy. Her clothes were reasonably priced, and loyalists—Françoise Hardy, Brigitte Bardot, Catherine Deneuve, the Countess Jacqueline de Ribes, and Claude Pompidou among them—bought knit skirts and trousers to wear with the sweaters; versatile bags; cloche hats that framed the face; and a cult-classic fragrance called 7e Sens, whose devotees Nathalie describes as “addicts.” Joan Burstein, president of Browns, which introduced Rykiel to the U.K., remembers her clientele as “the most elegant, well-known women in London.”

In a business predicated on perpetual novelty, Rykiel was a contrarian. She refused to participate in trends or even to set them. One season she would present stripes, and then, not long after, she would present stripes again. And again. Her colors, too, recurred, so that the next season’s blue matched the blue from three years before. Because, of course, the thing about fashion is that sooner or later it goes out of style, and Rykiel wanted to make clothes that would last. While most designers presented their collections on sullen, haughty goddesses who posed in a spotlight at the end of the catwalk, Rykiel sent her models down the runway in groups, chatting and laughing, like friends having fun. The cast hardly changed from one season to the next, and the models became members of her extended family. Ever since the youthquake of the ’60s, designers had geared their clothes to teenagers and 20-somethings, on the assumption that older women, wanting to look younger, would wear them, too. Rykiel refused to play along, making clothes intended for no age in particular, as becoming on an 80-year-old as on a young woman of 18. In an era that proved to be a watershed for women’s rights, she demonstrated alongside feminists and signed numerous petitions, including the famous “Manifeste des 343 Salopes,” a declaration published in 1971, written by Simone de Beauvoir and signed by 343 “sluts” who had had an abortion, which was illegal in France at the time.

Rykiel came to be known as an avid proponent of the notion that a lively mind could be sexy. While other designers stacked their front rows with party girls and movie stars, Rykiel commanded a broader audience—not only actresses (Anouk Aimée, Isabelle Huppert, Isabelle Adjani, Lauren Bacall) but also musicians (Gerry Mulligan, Leonard Cohen), politicians (Lionel Jospin, Jack Lang), writers and philosophers (Bernard-Henri Lévy, Pascal Bruckner, Nathalie Sarraute). In the tradition of the great salonnières, Rykiel entertained prominent thinkers from a variety of fields in her open-plan, loft-like Paris apartment, with its black lacquered walls, black carpet, low seating, silver bibelots, and myriad books. There were portraits of her by Andy Warhol and Cesar propped unceremoniously against the wall. Her shop windows became a platform where she showcased books—not coffee table fashion or photography books but novels, biographies, and collections of essays. Hours after the terrorist attacks on the staff of Charlie Hebdo, a satirical newspaper, in Paris this January, the windows featured the paper’s back issues and the work of Jean Cabut and Georges Wolinski, two journalists among the victims.

A writer herself, Rykiel has published more than a dozen works, including a novel, a children’s book, an abecedarian self-portrait in which 400 of her favorite words serve as points of departure for observations about fashion and life, and an epistolary exchange with her friend Régine Deforges, an editor, publisher, and outspoken author known for her erotic literature. In 2012, in a book called N’oubliez pas que Je Joue (“Don’t Forget That I’m Playing”), she wrote a moving account of her long struggle with Parkinson’s disease, which she tried to keep secret until she could no longer conceal the symptoms.

Few people today, if asked to name designers who were innovators, would cite Rykiel, and yet she was undoubtedly ahead of her peers when it comes to ideas and techniques that have shaped the course of fashion history. She did away with darts and hems, turned garments inside out, and exposed the seams’ raw edges way back in the ’70s—before revealed structure became a hallmark of the Japanese avant-garde. She put straps inside a coat, as Helmut Lang would do in the ’90s, so that the wearer could take it off when she got warm and carry it like a backpack. She collaborated with 3 Suisses, a catalog selling affordable fashion, in 1977, some 20 years in advance of other designers’ “mass” commissions for Target and H&M.

Rykiel built her empire in her own image, based on her instinct, principles, and personality. “We never discussed concepts or strategy for the brand,” says Dominique Issermann, the photographer whose advertising images during the ’70s and ’80s articulated the Rykiel style in a series of indelible portraits of women dressed in black against a black background. “We were talking about women, imagination, beauty, and irreverence.” Rykiel has been compared to Coco Chanel, for the obvious reason that both were designing for themselves, producing the clothes they wanted to wear, convinced that other women would want to wear them too. But the parallels run deeper: Both were petite and created styles whose proportions weren’t scaled to a runway model’s long limbs. Both were advocates of the high armhole, which kept Chanel’s jackets in place when, as a test, the fit model would swing her arms. Both Chanel and Rykiel loved jersey, and they elevated knits to new levels of sophistication, enabling women to be both well dressed and free to move. Despite the polished chic of their respective styles, Chanel and Rykiel were radicals, out to overthrow fashion while operating within it. Each invented a formula of sorts, equivalent to a man’s suit and appropriate for any number of occasions, that would relieve women of the obligation to come up with a new outfit every day and enable them to get on with their lives. Issermann recalls meeting one day with Rykiel in her office, when the designer’s P.R. rep interrupted to remind her that she needed to leave for Venice. A car was waiting to take her to the airport. Rykiel put on her marabou coat and reached for her handbag. “But where is your suitcase?” Issermann asked. Rykiel shrugged and said she would buy a pair of tights and a toothbrush when she got there.

With her on-the-go brand of chic, de Libran’s affinity with Rykiel’s style runs deep. Her design sense combines American ease, Italian artisanal techniques, and the decidedly French notion that dressing well is a courtesy one owes to others. “People in France care,” de Libran says. “It’s the culture and the education. You don’t show yourself if you’re not put together.” Her mother wore Rykiel, and the clothes made such an impression on de Libran that she likens the experience of going through the company archives to being a little girl going through her mother’s closet.

Born in France to French parents, de Libran grew up in Rancho Santa Fe, California, where her father had gone to pursue his personal version of the American Dream. He opened French restaurants and bistros and sold French breads and pastries, while her mother worked as an interior designer specializing in French antiques. On trips back to Paris, her mother would shop for clothes at Sonia Rykiel, who was also one of her father’s favorite designers. This, it seems, was not uncommon. Any number of women who wore Rykiel in the ’70s and ’80s claim that the men in their lives liked to see women in her clothes. “Rykiel dressed for herself,” de Libran says. “But she also dressed for a man.” While Rykiel’s designs were never blatantly seductive or revealing, the slinky silhouette she pioneered “is very flattering, very feminine,” de Libran notes. “It gives a nice proportion to the neck and definitely makes you look longer and thinner.”

After high school in California, de Libran left for Milan to study fashion at Istituto Marangoni and later designed for Prada, where she worked directly with celebrities, creating one-off outfits for the red carpet and experiencing the satisfaction that comes with pleasing the woman who will ultimately wear the dress. Then, in 2008, she moved to Paris to work at Louis Vuitton alongside Marc Jacobs. Meanwhile, the Sonia Rykiel label was undergoing profound changes. After Rykiel retired, in 2009, the house failed to find its footing for a few years as it experimented with different creative directors. When Jacobs exited Louis Vuitton to focus on his own line, de Libran jumped at the opportunity to take the reins at Rykiel.

De Libran’s debut collection featured a procession of jumpsuits, which she loves “because it looks like you’re wearing an evening dress, but you have that different attitude of wearing a pant—you sit differently, you move bigger, you walk faster. It’s a little less proper. I like that strength.” She also used denim and leather, two materials Rykiel hadn’t much explored, as well as fox and mink knitted into double-face sweaters as light as a cardigan. The house’s signature stripes turned up on everything from fur chubbies to organza peasant dresses and a bikini; military-inspired gear was repurposed as chic urban wear. Even the tailored jackets exuded offhand ease over skin-baring tops, echoing one of de Libran’s favorite vintage Rykiel pieces that she inherited from her mother: a double-breasted jacket with gold buttons, worn with nothing underneath and Bermuda shorts. “I think it’s still super-relevant,” de Libran says. “It doesn’t look retro at all.”

As if to invoke the spirit that pervaded the brand’s early days, de Libran chose to present her debut collection at the Rykiel boutique, in the same mirrored setting Rykiel used for her informal shows in the ’70s. The models included Georgia May and Lizzie Jagger (whose mother, Jerry Hall, was a Rykiel favorite), as well as Instagram-friendly newcomers like Gigi Hadid and Kendall Jenner. That night, instead of the usual fashion party, de Libran celebrated with a dinner in the upstairs room of the Café de Flore, to which only women, including her close friend Sofia Coppola, were invited. De Libran seems to genuinely enjoy listening to other women, discovering what they want, how they live, and how they see themselves. And unlike a number of designers who have taken charge of faded trademarks with no following and no notion in the public’s mind of what they stood for in the first place, de Libran finds herself with a sorority on her hands. Admittedly, there have been periods when membership was down, but the sisterhood is intact—and there is an entire new generation to recruit.

While many young designers take on subordinate roles to learn the ropes, preparing for the day when they open their own house, de Libran claims to have no burning ambitions when it comes to seeing her name on a storefront or a label. Though Rykiel herself is no longer a presence in the design studio, it is the style she created that will set the parameters in which de Libran works. “If people say, ‘It’s Rykiel,’ I’ll know I’ve done my job well,” de Libran says. “I really respect what she accomplished. Otherwise, I wouldn’t be doing this."

Watch: Sofia Coppola takes a tour of the Sonia Rykiel studio.