The dazzling output of designer Yves Saint Laurent is of such importance to the fashion industry that it's hard to know which of the many iconic points punctuating his career to use as the starting point.

There are simply too many.

In director Jalil Lespert's lush evocation of his life - Yves Saint Laurent - that starting point is Paris 1957 when Yves, aged 21, was catapulted to stardom as the head of design at Dior.

Saint Laurent, who died in 2008 at the age of 72, had a career of firsts - of great successes and terrible lows. He was the first designer to put black models on the couture catwalk. The first couture designer to make ready-to-wear credible with his Rive Gauche line. Like Coco Chanel before him, he subverted masculine designs, in his case the safari jacket, trouser suit and the tuxedo.

The film salutes his genius, explores his demons, and celebrates his enduring love affair with Pierre Berge.

Lespert says: "I wanted to do a movie about creation, genius, love and also an epic French story. He was ahead of his time - a true avant gardist. Yves was an amazing creative force, and I wanted to tell the human story behind the icon. He was bigger than life, bigger than fashion I would say, he upgraded everything because he was pure talent, pure generosity, he was like a poet."

Born in 1936 he grew up in Oran, Algeria. At 17 he left for Paris, where he beat Karl Lagerfeld into second place in a prestigious fashion contest, starting a lifelong rivalry between the two.

He was hired by Dior, who died two years later. Although it might have seemed a great risk placing such a prestigious couture house in his young hands, Yves was already well established in the Dior atelier. One of his earliest creations, a black column with white sash is featured in the iconic Avedon photograph of Dovima with Elephants and the 1957 Dior's Fall couture collection, shown shortly before Dior's death, featured 35 of his outfits.

But dark days lay ahead and in 1960 he was conscripted into the French army. Sent to Algeria to fight, he suffered a nervous breakdown and was admitted to a psychiatric hospital in Paris. While sedated and undergoing shock treatment he was replaced at Dior. His partner Berge fought to secure his release from hospital in 1961 though the nightmarish experience left an indelible emotional scar.

The actor Pierre Niney prepared for almost half a year to play Yves Saint Laurent and even learned to sew and draw. He says: "His life shows us how strength, shyness, joy and desperation can inhabit one man. I loved that idea that Yves managed in the worst moment of desperation and pain to transform his suffering into masterpieces.

"There were three big tests. One to portray a sick man, Saint Laurent was diagnosed as a manic depressive at the age of 22. Then there was the aging process; I play him from the age of 18 to 46, and finally the radical evolution of Yves's style and fluctuating states of mind."

The film uses 77 key archive pieces and Lespert says: "There was twice as much work on the costume design as there usually is on a film. We had to design the period costumes to reflect the changing trends in fashion over those 20 years. We were lucky enough to be able to use original costumes.

"Once we found the right models - which was a real hassle as models had a different build to girls today, they were extra slender back then - it was fantastic, although painstaking as the girls could only wear the dresses for two hours in a row to preserve them. And they couldn't sit down!"

Filming the penultimate scenes were a highlight for Lespert. "Pierre Berge was on set, the only day he was there. He was right next to me, and when Niney took his bow as Yves, I looked over at Berge and he was crying. It was really moving."

Berge said he was "blown away" by Niney's portrayal of Yves. "It really disconcerted me. At times I thought it was Yves Saint Laurent himself. That's huge."

Yves Saint Laurent (15) is in cinemas now.