In a consumer culture that burns through trends faster than they can emerge, it is almost impossible to imagine one fashion designer having an impact on an entire generation. Yves Saint Laurent, who died at 71 yesterday, did just that.

His importance can be put in perspective with institutional markers: The French awarded him the Legion d’Honneur in 1985 and the Metropolitan Museum of Art made him the first living designer ever to have his own retrospective. He was tapped to helm the haute couture house of Christian Dior at age 21.

Ultimately, he was the man who put women in trousers — and made it not only sexy and chic, but acceptable.

Saint Laurent maintained the traditions of haute couture while in charge at the hallowed, sacred halls of Dior, which defined the French understanding of chic. But it was only after 1962, when he opened his own couture house and later started his own chain of ready-to-wear boutiques, Rive Gauche, that his influence and importance spread. Saint Laurent’s “Le Smoking,” or tuxedo, jacket, which he introduced in 1966, was a pivotal point in fashion. Tradition was being torn asunder, and the rules were there to be broken. By transposing menswear onto womenswear, Saint Laurent brought fashion in line with the youthquake and cultural revolution. As Godard and Truffaut were modernizing film, Saint Laurent was modernizing the female wardrobe. As the Beatles were redefining popular music, Saint Laurent was redefining style.

His popularity came at a time when the idea of the modern celebrity was taking hold; He was part of a milieu that defined what it was to be young, fabulous, Parisian. And along with his longtime lover and business partner, Pierre Berger, he was at the forefront of establishing what would become a global fashion brand with licenses for everything from perfume to mens clothing.

Indeed, from its inception to its corporate ownership today, the house that Saint Laurent and Mr. Berger built is at the center of the history of fashion. Founded by its initial talent, the brand created an identity that made it attractive to corporate interests. In 1999, the house was purchased by the Gucci Group. Tom Ford, who was creative director of Gucci at the time, oversaw the brand’s evolution into the corporate world.

The transition was rocky, and Saint Laurent retired in 2002. At that time, Mr. Berger worked to preserve the designer’s legacy with a foundation. A beautiful Paris mansion in the Rive Gauche serves as a museum where illuminating exhibitions of past collections are presented. Drawings and sketches that Saint Laurent made for not only commercial clothing but also stage costumes line the walls. The foundation preserves more than 5,000 items of clothing; some of which were samples from couture collections and others that were pieces donated from collectors who bought them in decades past. What’s most impressive about the foundation is that through its devotion to one man’s legacy, it is preserving the history of fashion with as much seriousness as other museums preserve works of art.

[Born in Algeria on August 1, 1936, Saint Laurent showed an early interest in clothes and at the age of 17 won first prize in a contest sponsored by the International Wool Secretariat for a cocktail dress design, the Associated Press reported.

A year later in 1954, he enrolled at the Chambre Syndicale school of haute couture, but student life lasted only three months. He was introduced to Christian Dior, then regarded as the greatest creator of his day, and Dior was so impressed with Saint Laurent’s talent that he hired him on the spot.

When Dior died suddenly in 1957, Saint Laurent was named head of the House of Dior. The next year, his first solo collection for Dior — the “trapeze” line — launched Saint Laurent’s stardom. The trapeze dress — with its narrow shoulders and wide, swinging skirt — was a hit, and a breath of fresh air after years of constructed clothing, tight waists and girdles.

In 1960, Saint Laurent was drafted into military service — an experience that shattered the delicate designer, who by the end of the year was given a medical discharge for nervous depression.

Bouts of depression marked his career. Pierre Berge, the designer’s longtime business partner and former romantic partner, was quoted as saying that Saint Laurent was born with a nervous breakdown.

When he bowed out of fashion in 2002, Saint Laurent spoke of his battles with depression, drugs, and loneliness, though he gave no indication that those problems were directly tied to his decision to stop working, the Associated Press reported.

“I’ve known fear and terrible solitude,” he said. “Tranquilizers and drugs, those phony friends. The prison of depression and hospitals. I’ve emerged from all this, dazzled but sober.”]