Watching from the front row, the fashion editors attending Yves St Laurent’s "Pop Art" collection in August 1966 weren’t overtly enamored with what they saw.

Influential New York Times critic Gloria Emerson, suggested the designer “strains too hard to convince the world he is hand-in-hand and eye-to-eye with the very young,” and deemed the collection “lumpy” and “outdated."

The slim-line fur coats and dresses inspired by the contemporaneous art of Roy Lichtenstein and Andy Warhol drew the most attention with a lukewarm response. Fast-forward 45 years, and it’s clear that what was actually unveiled that day at 5 Avenue Marceau, Paris was one of the most influential and iconic designs in 20th century fashion history.

We’re talking about Le Smoking, the first tuxedo for women. It consisted of a classic dinner jacket in black grain de poudre wool or satin and trousers with a satin side-stripe with a ruffled white shirt, black bow tie and a wide cummerbund of satin.

This was a bold evening wear alternative to the little black dress by the Algerian-born designer. Despite the so-called "second-wave feminism" of the 60s, encouraged by developments like the availability of the contraceptive pill, well into the decade it was still controversial for a woman to wear trousers in public.

Few respectable restaurants or hotels allowed female guests to wear them inside. Nan Kempner was famously turned away from Le Côte Basque in New York while wearing her YSL tuxedo suit. Yet in the defiant style befitting of this androgynous, no-nonsense look, she removed the bottom half and waltzed into the restaurant wearing the jacket as a thigh-skimming mini dress instead. The manager later said that for formal dining attire trousers were as unsuitable as a bathing suit.

So, dressing in a YSL trouser suit declared the wearer was irreverent, daring and on the cutting of fashion, whilst suggesting their alignment with burgeoning feminist politics—le smoking effectively demanded: "If men can wear this, why can’t I?"

Saint Laurent was influenced by the avant-garde style of artist Niki de Saint-Phalle, who reportedly often wore men’s suits with heels, as had Greta Garbo and Marlene Dietrich in the 30s.

Coco Chanel memorably designed loose trousers for women in the early 20th century, while during the Second World War they were widely worn while taking on manual labour in their husbands’ absence. However, Saint Laurent was the first high profile couturier—the designer who had taken the reigns great House of Dior, no less—to promote this aesthetic for high fashion evening wear and heightened the impact by offering not just trousers but a slick, monochrome take on the classic tuxedo, usually worn to the most formal black-tie events.

The fashion buyers and editors may have missed a trick in 1966, but a handful of chic female stars in Saint Laurent’s milieu, such as Catherine Deneuve, Liza Minnelli, Lauren Bacall and Bianca Jagger, instantly took to this daring new silhouette. Models photographed by Helmut Newton in 1975, styling Le Smoking with slicked back hair and masculine posture, helped disseminate Saint Laurent’s creation and engrain it as an iconic image in the public imagination.

Le Smoking became such an icon that the brand ensured that some manifestation of it was included in every subsequent fashion collection, continuing up to present day with the YSL’s current head designer, Stefano Pilati. Over the years, the tuxedo suit has reappeared in a huge variety of guises and fabrics: reworked as a dress or trench coat, given a bolero in place of a jacket and shorts instead of trousers, incarnated in velvet, silk or leather.

It was the original 1966 Le Smoking that remained the designer’s personal favorite, though. At the close of his haute couture atelier in Avenue Marceau in 2002, this version was the very last piece to be made there (ordered by Sir Paul Smith for his wife Pauline, in fact).

Saint Laurent himself attributed the enduring appeal and iconic status of Le Smoking to the fact it encapsulated an attitude or mode, rather than any particular details of the garment. “For a woman, le smoking is an indispensable garment with which she finds herself continually in fashion, because it is about style, not fashion. Fashions come and go, but style is forever.”

Le Smoking was just one of the many iconic, original looks pioneered by Yves Saint Laurent; here are four more of his greatest fashion moments...

The Safari Jacket

In 1968 the supermodel Veruschka posed in a beige cotton jacket, with a seductive lace up bodice and a silver loop belt. Another signature look was born, which, like Le Smoking, he reinvented again over the ensuing decades, including the 1982 version with a longer peplum and heavier gabardine.

The Mondrian Dress

The classic 60s shift with its simple, planar form was an ideal blank canvas for Saint Laurent to play with bold block prints in the same vein as modern constructivist artists like Pierre Mondrian. The beguiling jersey dress hid its structural tailoring inside the colorful grid of seams. Straddling the fields of fashion and painting as it does, the dress features in the permanent collection of the Metropolitan Museum of Art, New York.

Haute Peasant/Ethnic

Beaded raffia dresses, tribal-style prints and a variety of fringed, woven and tressed pieces in his preceding 1967 collection revealed the deep influence of African art on his imagination. Before long, mainstream stores were awash with ethic-inspired fashion. His haute peasant look of the mid-70s, inspired by eastern folk art and labeled the ‘Ballet Russe’ collection, similarly had affluent fashionistas coveting the embroideries, full skirts, heavy costume jewelery and beading of Bohemia.

The See-Through Blouse

Characteristic of Saint Laurent’s titillating, insouciant approach to fashion design, he debuted risqué transparent fabrics in his 1966 collection. In keeping with the new mood of sexual freedom and playfulness of the 60s, the sheer organza dress revealed the model’s breasts.