updated 5:33 p.m. ET June 2, 2008

Yves Saint Laurent changed the way women dress more than they know.

The Algerian-born designer, who died Sunday at age 71, was the champion of beatnik black, pop-art prints, safari jackets and peasant skirts still fashionable decades later. But his most enduring legacy is so pervasive as to seem almost unremarkable: pants.

Saint Laurent's elegant pantsuits broke barriers between the sexes, a sartorial revolution that fit a social one and changed the way generations of women dressed.

"For a long time now," he said upon his retirement in 2002, "I have believed that fashion was not only supposed to make women beautiful, but to reassure them, to give them confidence, to allow them to come to terms with themselves."

He was one of the most influential designers during the most important era of Parisian fashion, Christian Dior's hand-picked successor and a peer to Coco Chanel and Cristobal Balenciaga.

"Every woman in the world, sometimes without even knowing it, has something in her closet inspired by Yves Saint Laurent," said the American designer Michael Kors. "His genius is irreplaceable."

Saint Laurent's signature was taking menswear silhouettes and slimming them down to fit a feminine shape. He may not have been the first to put a woman in a trenchcoat or safari jacket, but "they're indelibly associated with him because of the spin he gave them for the modern woman," said Valerie Steele, director and chief curator of The Museum at the Fashion Institute of Technology.

"Everyone wanted to be Yves Saint Laurent. He was such an unbelievably gifted man," Oscar de la Renta said by e-mail. "He was a great innovator and some of his trends, like the smoking suit, are as influential today as when he first designed them. He just had an extraordinary eye for fantasy and every woman wanted to be a part of that world."

Privately, though, Saint Laurent struggled with depression and drugs.

"You shouldn't believe Saint Laurent was a happy man," said close friend and longtime business partner Pierre Berge. "He was unsatisfied, anxious. A man who had trouble achieving what he wanted, out of perfectionism, precisely."

Berge called Saint Laurent "very, very demanding with himself."

Video   Fashion world bids adieu June 2: The fashion world marks the passing of Yves Saint Laurent. Msnbc.com's Dara Brown reports. msnbc.com

"The night before a show, he could have the sleeves changed completely — for a millimeter, a millimeter! — and we could work all night in the ateliers until the morning's presentation. ... For him, there was no question of doing things otherwise. It was an imperial, extraordinary kind of perfectionism."

Saint Laurent became a star in 1958 with the trapeze dress — with narrow shoulders and wide, swinging skirt — in his first solo collection for House of Dior, a year after taking over following Christian Dior's sudden death.

When Saint Laurent launched his own label in 1962, he understood that within most women lived two styles: the practical one who needed clothes to get things done, and the flirt who needed peek-a-boo tops and minidresses.

"Yves was the most influential designer working in the '60s and '70s, which were the years that I was growing up and forming my own taste and sensibilities, so he had a tremendous effect on my visual world," said Tom Ford, who took over the YSL ready-to-wear runway in 1999 when Saint Laurent sold his fashion house to the Gucci Group.

The first YSL tuxedo for women (also known as "Le Smoking") surfaced in 1966, paving the way for future stylish pantsuits. His 1960s' "chic beatnik" look — black leather jacket, knit turtleneck, high boots — was initially met with bad reviews but became a classic.

Then there were his "art dresses," such as the minidress printed in bright squares that evoked Piet Mondrian's geometric works. His peasant-chic "Ballets Russes" collection dazzled Paris, and Saint Laurent also was among the first to mine China and Africa for inspiration.

"He was like Picasso in the way he kept transforming his style, and yet each new one had an incredible impact on fashion," said FIT's Steele.

While a master of couture, Saint Laurent also paid great attention to ready-to-wear fashion with his then-groundbreaking Rive Gauche collection, realizing that even some of fashion's most devoted fans were losing the time and taste for elaborate custom-made clothes.

At the root of it all was a deep affection for women. His mother was an inspiration to him and a fixture at his fashion shows and wore nothing but Yves Saint Laurent designs.

"She was the one I thought of first this morning on learning that he had escaped the suffering of a world that resembled him less and less, to join the pantheon that is his," designer Christian Lacroix said Monday.

Tributes poured out from fellow designers, including old friend Valentino, who expressed admiration for "his sense of fantasy and his great respect for women and beauty." Giorgio Armani hoped to remember Saint Laurent as more than "the foremost and truest designer of our time."

He described a private visit to Saint Laurent's "museum-like" home in Marrakech. The Italian designer arrived "in a run-down minibus rented from a travel agency wearing shorts and a T-shirt which I could see immediately made him feel somewhat perplexed as he stepped out to greet us in a most elegant pinstriped double-breasted suit."

"After just half an hour's conversation however, he was talking to me like you would speak to an old friend taking me into his confidence. Then on saying our goodbyes he urged me to return to see him again soon."

Saint Laurent's brand lives on without him. By the time he officially retired in 2002, he had already sold his fashion house to the Gucci Group in 1999. Stefano Pilati is now at the helm of YSL Rive Gauche.

But with his death comes the close of an era — a time when a runway show could send shockwaves across continents.

"It is the end of a certain kind of a designer, the last of the Chanels and Diors, designers with an amazing international impact on fashion," Steele said.

In part, that's Saint Laurent's own doing. He broke so many barriers that few remain; the industry has become more concerned with what sells, following his ready-to-wear influence; and Paris' star in the fashion world has dimmed under the global influences he embraced.

Pamela Golbin, curator at the Fashion Museum (Musee de la Mode) in Paris, said Paris will always remain a center of fashion, but that something is forever lost without Saint Laurent: "A chapter is closing."

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