Legendary fashion designer Yves Saint Laurent has died aged 71, his long-time friend and former partner said.

Pierre Berge did not give details but said the couturier died at his Paris home last night following a long illness.

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A towering figure of 20th-century fashion, Saint Laurent rewrote the rules of fashion by putting women into elegant trousersuits that came to define how modern females dressed. He was widely considered the last of a generation that included Christian Dior and Coco Chanel and made Paris the fashion capital of the world, with the Rive Gauche, or Left Bank, as its elegant headquarters.

In the fast-changing world of haute couture, Saint Laurent was hailed as the most influential and enduring designer of his time. From the first YSL tuxedo and his trim pantsuits to see-through blouses, safari jackets and glamorous gowns, Saint Laurent created instant classics that remain stylish decades later.

When the designer announced his retirement in 2002 and the closure of the Paris-based haute couture house he had founded 40 years earlier, it was mourned in the fashion world as the end of an era. His ready-to-wear label, Rive Gauche, which was sold to Gucci in 1999, still has boutiques around the world.

Saint Laurent was born on August 1 1936, in Oran, Algeria, where his father worked as a shipping executive. He first emerged as a promising designer at 17, winning first prize in a contest sponsored by the International Wool Secretariat for a cocktail dress design.

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 at 21. 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. Mr Berge, the designer's business partner and former romantic partner, was quoted as saying that Saint Laurent was born with a nervous breakdown.

Saint Laurent returned to the spotlight in 1962, opening his own haute couture fashion house with Berge. The pair later started a chain of Rive Gauche ready-to-wear boutiques.

Life Magazine hailed his first line under his own label as "the best collection of suits since Chanel".

Nowhere was Saint Laurent's gift more evident than the valedictory fashion show that marked his retirement in January 2002.

Forty years of fashion were paraded in a 300-piece retrospective that blurred the boundaries of time, mixing his creations of yesterday and today in one stunning tribute to the endurance of Saint Laurent's style.

His "smoking" or tuxedo jacket of 1966 remade the tux as a high fashion statement for both sexes. It remained the designer's trademark item and was updated yearly until he retired.

Also from the 60s came Beatnik chic - a black leather jacket and knit turtleneck with high boots - and sleek trousersuits that underlined Saint Laurent's statement on equality of the sexes. He showed that women could wear "men's clothes" which when tailored to the female form became an emblem of elegant femininity.

Some of his revolutionary style was met with resistance. There are famous stories of women wearing Saint Laurent trousersuits who were turned away from hotels and restaurants in London and New York.

In 1999, Saint Laurent sold the rights of his label to Gucci Group, ceding control of his Rive Gauche collection, fragrances, cosmetics and accessories for £35 million cash and royalties.

Industry insiders cited friction between Saint Laurent and Gucci's creative director, Tom Ford, as a likely factor in the fashion guru's decision to retire three years later.

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.

"I've known fear and terrible solitude," he said. "Tranquillisers and drugs, those phoney friends. The prison of depression and hospitals. I've emerged from all this, dazzled but sober."