A chill wind is blowing across north-west London, sending litter scattering over the railway tracks and used-car lots of Willesden Junction. Inside a windowless, white-fronted building, next to a printer’s and overlooking a cemetery, it is nearly as cold. The ancient blow heater has broken down and a cavernous space is warmed only by electric lights, hanging from the ceiling like glowing caterpillars.

A rake-thin figure is at one side of the room, grasping a scaffolding tower for support. Rhythmically, she pushes her feet forward, standing on first one leg, then the other. The toes flex and furl, brushing the ground, every muscle at work. Slowly the movements increase in intensity. She raises her legs to the front, to the rear, to the side, letting them fly ever higher, twisting out from the hips so they mark circles in the air.

For 39 years, a variation of these exercises has started Sylvie Guillem’s day. This routine of tendu, rond de jambe, and port de bras began when she was a “little rat” at the Paris Opera Ballet School, her bright hair tied back in a neat bun. They continued through her rise to become the youngest ever étoile in the company, through her gleaming years as a ballerina at Covent Garden and as a guest star around the world. They have sustained her as she ventured into daring new terrain, performing works from contemporary choreographers, and extended her career beyond any normal expectations.

Now, the most important dancer of her generation, the woman who changed ballet for ever, is coming to the end of that life. In December, at the age of 50, she will retire, never to dance again. Having built an entire career on sticking to her guns, she has made one final choice. But first there is one last tour, with two all-new works to create and learn. “I didn’t want to do a Best Of,” she says, smiling. “I wanted to carry on exploring. I like creation even if the process is always a bit difficult. It’s always very exciting, and also less sad than just to go back. Why do again what I have already done?”

So here she is, in icy January, in this big, bare room, muffled up in layers, topped by dungarees with braces, a big white shirt, loose jacket and scarf, her long red hair pulled back in a plait, working from 10am to well past 7pm with the choreographer Russell Maliphant, who is creating a new duet for her and the Italian dancer Emanuela Montanari. Guillem puts on and strips off garments depending on the level of exertion and the temperature in the studio; as each section of dance is made, Maliphant records it on a laptop. At regular intervals they pause to watch and analyse its effects, reading glasses perched on their noses, like two professors.

“They are hinged into my life, those people”: In PUSH, by and with Russell Maliphant, a regular collaborator, at Sadler’s Wells in 2005

This as yet untitled piece is their fourth collaboration. Guillem approached Maliphant in 2003 because she liked the way he made people move; her interest in creating new work has always been propelled by a desire to feel, in her bones, different ways of moving and seeing. It’s an impulse that has made her commission the other choreographers whose work features in her farewell bill: Mats Ek, William Forsythe, Akram Khan. “They are hinged into my life, those people. They are creative people and I want to go into their world, into their mind and also the way they see me. That is what is important.”

Today, getting into Maliphant’s mind is proving a struggle. “You want to give me shit?” she asks, when he suggests a complicated turn. But she laughs as she says it, and carries on endlessly repeating the moves until they are both satisfied. Then she talks to Montanari—in Italian—working through the steps with her, acting as teacher and translator. At times they look like Pippi Longstocking and her little sister, heads together, giggling and grimacing as they strive to learn. Occasionally, they both lean forward, hands on knees, to catch their breath. The atmosphere is one of calm concentration—a mood broken by the arrival of Michael Hulls, lighting designer and Maliphant’s constant collaborator, who brings the dark news of the Charlie Hebdo shootings. “What a world we live in,” says Guillem, as they break for lunch.

Sitting at a formica table, eating crackers and kale soup, she talks about violence and the political situation in France with dismay in her voice. It is not the kind of conversation you often hear in the etiolated world of dance, but Guillem likes to engage with society. She is vegan, on the grounds that “I do not want an animal to die for me”, and a strong supporter of the eco-campaigners Sea Shepherd, who use direct action to draw attention to illegal whaling and the destruction of the oceans. She uses her fame as a weapon to highlight such causes—her last tour, “6,000 Miles Away”, visited tsunami-stricken areas of Japan to point to their plight and raise funds.

In “Sacred Monsters”, the duet she made with Khan in 2006 which was the first time she had spoken on stage, there is a moment when she tells the story of Sally in the “Peanuts” cartoon. She is skipping happily away, then suddenly bursts into tears. Guillem says she knows how Sally feels—both the exhilaration of the skipping, and the sudden realisation of pointlessness.

“It’s the balance,” she says. “Yes, it’s futile what we do, but it’s part of a positive thing. We are not doing wrong, we are not killing, we are not hurting people, we are not exploiting people, we are not lying. There is something true and genuine about it, so in the end it is important. But the thing is, you must do it as well as you can.”

So that is what she does, dancing on under the lights Hulls has assembled, tracing the steps with Montanari when everyone else has left. Even in a drab rehearsal space, she shines; movement seems to spring from the centre of her being and flow to the tips of her fingers. “That line doesn’t stop at the end of her body,” says Maliphant. “It goes out into space. She has been thinking about aesthetics and line and how she looks since she was very young. She can make extraordinary shapes with such ease. It is just part of her.”

S ylvie Guillem never wanted to be a ballerina. She was a gymnast who ended up at the Paris Opera Ballet School on a year-long exchange programme, designed to give athletes added polish. “I was lucky because I had a different status. In the boarding school, from Sunday evening to Friday evening, you are watched all the time. But there were three of us who, three times a week, could escape, take the Métro, go to the National Institute of Sport and train as gymnasts. So we had this little different life, and didn’t have the same mentality of the others. I didn’t really understand that mentality. It was a strange tension. The notion of pleasure was not there at all.”

She describes the teachers, with heavy emphasis, as “witches”, but she didn’t care. Unlike her two friends, she found ballet class easy, and then one day she was invited to take part in the end-of-year performances. “Curtain up. That was it,” she says, with ringing simplicity.

We are talking on Saturday at 7pm in a crowded hotel bar; Clerkenwell is getting geared up for a night on the town. For Guillem it will be supper, a massage and bed. She has been in rehearsal all day. Even at lunch in the Sadler’s Wells café, she didn’t get the chance to relax: she had to clean up a table to make herself space to sit down. Now, make-up free and relaxed, she looks tired but seems happy to look back on her career with the honesty that is her hallmark.

From that moment of revelation at 11, she was destined to be a ballerina. She fixed her eyes on the prize and coped as best she could with the restrictive discipline. “You learn about people, and betrayal and stupidity,” she says, pulling a wry face. “But I knew something was there for me. I really enjoyed the stage. The rest, no, but if you have to go through that to get there, OK fine, you do it. Also it was not very difficult for me. I was lucky. Every year, I came top in the exams. What was in my mind was passing every test, and then getting into the company to see what was interesting there. Just that.”

At 15, she went on tour to Japan with the Paris Opera Ballet School and her virtuosic performances made audiences laugh with pleasure. “It was the moment I discovered the impact I could have. It was like, wow, what have I done? And this I like. This I really do like.”

Nureyev soon saw that, hidden in the corps de ballet, he had a generation of dancers who could shake the world

Then in 1983, Rudolf Nureyev arrived as director of the Paris Opera Ballet, determined to shake up a venerable institution that had become sclerotic. He soon saw that, hidden in the corps de ballet, he had a generation of dancers who could shake the world. They were waiting their turn for promotion, but Nureyev was having none of it. He understood that time is never on a dancer’s side. On December 29th 1984, after a matinée performance of “Swan Lake”, he called every­body on stage and announced that he was making Guillem an étoile. At 19, she was the youngest in the company’s history.

What did she feel? “Relief. It was like, OK,” she claps her hands, “I’ve done it, now let’s start the serious thing. It was really the beginning.”

And what a beginning. This young woman, with beautiful green eyes, and a body that was strong and supple at the same time, was about to start a revolution, throwing open the closed shutters of ballet to let in some new, fresh air. William Forsythe vividly remembers the first time he saw her. “My assistant said, ‘You’ve got to see this girl,’ and we went to peer into the studio through a little window at the back. There she was, doing her barre exercises at the piano. She was amazing.”

In 1987 he put her at the centre of “In the Middle, Somewhat Elevated”. Its extreme neo-classicism was like an electric shock: Guillem strutted across the stage with a kind of insolence, holding off-kilter poses with power and panache. “She had a gift so large that it defined and instigated a new epoch of how we perceive possibility,” Forsythe says. “But she never just whacked her leg up because she could. It was an idea, an aesthetic choice that she consciously made and she changed the ballet world with it.”

The effect of Guillem’s line, her ability to stretch one leg up to her ear like a clock striking six, has been endlessly debated. For a handful of critics, it was vulgar, a distortion of the academic perfection of classical ballet. But for audiences it was thrilling, and for other dancers it was inspiring. “How can you ask an artist, someone who had this ability, not to use it?” says Tamara Rojo, then a Covent Garden colleague, now director of English National Ballet. “It is like saying we all know we can fly on a plane, but let’s take a horse and carriage instead because that’s what we have done before. Her decision has changed how we dance, the speed of how we dance and the range of emotions that you get from a body using all of its power. I don’t think people realise the emotional impact it had.”

“Curtain up, that was it”: Guillem at 20, in her dressing room for "Swan Lake" at the Paris Opera, 1985

Guillem is both unperturbed and quietly defiant about the fuss. “I wasn’t trying to use my legs in an ordinary or vulgar way. Sometimes I went over the top, but only when it was funny to do it, like in the Grand Pas Classique, which is a ballet that is completely kitsch,” she says, with some force. “But I never used it as a trademark. I always had respect.”

Anthony Dowell, then director of the Royal Ballet, remembers the impact she could have in the Grand Pas Classique. When she came to London as a guest, he was watching from the wings. “It was a complete surprise. There she was in that black lace tutu with a red bob wig; it was slightly irreverent but done with this incredible wit and subtlety. And this phenomenal technique. I remember, at the end, putting my hand round that lace waist and saying ‘Dear Sylvie, perhaps you could give the Royal Ballet a little more of your time.’”

That was in 1988 and Guillem was ready to move. For all the adulation, her rise to the top of the Paris Opera Ballet had not been easy. “When you start, you have no brain, you are a kid. It’s fine. But then I started to be scared. I was scared of judgment—not as a dancer, but as a person—and I was really uncomfortable with people. And it lasted for a very long time. People thought I had no feelings, that I was hard. But really I was extremely sensitive to everything.”

She adored Nureyev. “He was a great man. I am happy to think we understood each other.” But they clashed about the choices he made for her. “I liked to fight back because, for me, it was not a challenge but an automatic response to something I thought was unfair. I can’t stand what is unfair.”

Their arguments were exacerbated by her determination, from the first, to take charge of what she wanted to do as a dancer. This is rare enough in life; in dance companies, which are built on compliance and obedience, it is almost unheard of. “She was the first ballerina to take her career into her own hands,” Forsythe says. “I think that alone is worth gold.”

So when the Paris Opera refused to allow her even a minimum of freedom, and Dowell and the Royal Ballet offered a contract that gave her choices, she jumped. In 1989, like Nureyev before her, she became Principal Guest Artist with the Royal Ballet.

A nother week, another rehearsal room. This one is at the headquarters of English National Ballet, tucked into a mews behind the Royal Albert Hall. That makes it sound rather more glamorous than it is; this building too has seen better days. Faded photographs of famous dancers hang on the walls, but the girls in tutus who peer through the window know they are watching a living legend. What they see is a woman who has refined her life to its essentials. There are monks who live more lavishly than Sylvie Guillem.

Each day, she arrives with the minimum of clutter: a bag, shoes, elastic tape to wrap around her toes and her knees, a battered iPod full of teach-yourself-Japanese and Italian lessons, a Rolex watch on a heavy silver bracelet, a water bottle, her phone, her glasses.

She cooks her own lunch. She runs her own diary. She has no assistant. The nearest she comes to an entourage is the occasional presence of her partner

She cooks her own lunch. She runs her own diary. She has no assistant. The nearest she comes to an entourage is the occasional presence of Gilles Tapie, the photographer who has been her partner and support for more than 20 years. Together they celebrated her 50th birthday on February 25th with a quiet dinner in at her London hotel.

Today, she is working with Akram Khan on a piece about the relationship between humans and technology. At this early stage it involves Guillem and a microphone stand in the Heath Robinson tradition, with plugs and wires taped hair-raisingly across the studio floor. The choreography is sharp and fast, and created at the same time as the music—so three musicians are nestled in a corner of the studio, squeezed between stacked chairs and an unused piano, with computers, microphones, a violin and an Indian drum kit. Both the sounds and the steps are fantastical, requiring Guillem to make complex shapes with her hands and then rear like a racehorse.

At the end of the first run-through, including one passage where she rolls around the floor, she falls at the foot of the microphone, panting. “I like that ending,” says Lucy Carter, the lighting designer. Guillem laughs. She has great lightness, making fun of herself, defusing tension with self-deprecation. “I’m trying to do it right, that’s what’s so tragic,” she says, as Khan queries her timing. Later that day, she tells the musicians that the problem for ballerinas who retire is that they end up looking like bumblebees, with skinny legs emerging from rounded bodies. She mimics their splay-legged walk as she speaks. But this good humour comes with a steely resolve and a capacity for hard work. She is always the first to start and the last to finish, repeating steps relentlessly until she is satisfied. Most days, her attitude takes its toll; she limps around clutching an icepack on her hip or ruefully examining her bruises.

When you see her rehearse, you wonder how she ever acquired a reputation as a diva. She is not just different from her reputation; she bears little resemblance to it. “She is insanely generous,” says William Forsythe, “and has one of the finest work ethics I have ever encountered.”

Tamara Rojo agrees: “It was a privilege to be in the same studio as her. She was more demanding with herself than with anyone else. For her the art is something that demands all of you, your emotional commitment, your physical commitment, your intellectual commitment and your passion.”

“For young dancers watching her, it was incredible,” says Dowell, of Guillem’s time at the Royal Ballet. “To have such an inspiration in one’s midst.” Yet it was he who called her Mademoiselle Non—a nickname that has hung around her career like a bad smell. Does he regret it? “It was done in jest,” he says, with some emphasis. “I adore the woman and I hope she knows that. It was just the British sense of humour.”

It is true that Guillem herself has taken it in good part; she admires Dowell and invited him to dance with her on tour after his retirement as director in 2001. She found the repertory of the Royal Ballet rich and rewarding, putting her own stamp on roles such as the bored housewife Natalya Petrov­na in Frederick Ashton’s “A Month in the Country” and—famously—becoming the first ballerina since Margot Fonteyn to dance “Marguerite and Armand”, his dramatic miniature about the doomed courtesan Marguerite Gautier.

“They wanted to make me feel a bit small,” she says. “But I don’t care. I had the right to say no—why would I move from Paris to do the same thing?” She feels she is more patient and more tactful now. But as a young dancer, in a strange country and a new language, she struggled. “I was not happy in that I didn’t understand the English way. They asked me to come and then they didn’t use me as they could have.”

This was particularly true with Sir Kenneth MacMillan, the choreographer who was the most respected figure in the Royal Ballet when she joined. She was a magnificent interpreter of his Manon and Juliet—among her favourite parts to this day—yet their lack of communication was legendary, and revealed to all in a vicious clash that was accidentally broadcast over the tannoy. Part of the problem, Dowell feels, was that Guillem did not see that in the Royal Ballet the choreographers “were gods and they ruled the roost”. She could be implacable. “I didn’t have any impression of her being vulnerable,” Dowell says. “She was out for what she felt she wanted and she had quite a brusque, blunt way of dealing with things.”

The relationship with MacMillan foundered from the start. “What went wrong was that I said no to some of his ballets,” Guillem says, “and then he started to insult me. He said I was a boring French star. Each time I went to rehearsal, he put on his glasses. I think I was like an intruder in the family.” But why did she change his choreography, and so incur his wrath? “To make it logical, to adapt it to me, so I could do something with it. It’s like wearing something that doesn’t fit”—she pulls at her T-shirt. “You can’t work like this in ballet. You have too much responsibility to make it work. You are responsible for what you are doing at that moment on stage.”

This belief lies at the heart of Guillem’s dancing life. She has an almost Platonic image of what dance should be and she wants to communicate it. It comes back to that truthfulness again; she will fight for what she believes. Anything else isn’t worth the candle in her eyes. “I feel I am lucky to have the facility that I have, and I am doing it for a good reason. People want to see me, they buy their tickets. They deserve my honesty towards the work I am doing. I don’t want to disappoint them. I really care about that.”

O ne of the first words Alistair Spalding, the director of Sadler’s Wells, said to Sylvie Guillem was yes. “I remember it quite distinctly. It was when she came to dance ‘Broken Fall’, the first piece choreographed for her by Russell Maliphant. I walked on stage and she made a beeline for me because there was something she wanted. And I did it. From then on, there was a sort of trust. I make sure she gets what she needs to do what she needs to do.

She makes demands because she has high expectations of herself and everybody else. They are never unreasonable. She’s not a diva

She makes demands because she has high expectations of herself and everybody else. They are never unreasonable. She’s not a diva, she’s just very focused.”

That was in October 2004, when Guillem was beginning to find herself at odds with the artistic decisions of the Royal Ballet’s new director, Monica Mason. In 2006 she became an associate artist at Sadler’s Wells. In 2007, without fanfare, she left the Royal Ballet for good—and devoted herself to the last surprising flowering of her career. For Guillem herself, there has never been any difference between what she is doing now in contemporary dance and what she did in the world’s great ballet theatres. She returned to the three-act classical ballet when she danced “Manon” at La Scala in 2011, revealing an undimmed ability to give physical realisation to thinking and feeling. But the contemporary works she has commissioned and developed in the past decade have allowed her searching intelligence new and fascinating play. “Sylvie would not be Sylvie”, says Khan, fondly, “if she weren’t trying to throw herself into the deep end.”

Now that too is reaching its conclusion. She decided to retire quite suddenly, as her half-century approached. “Time is time, age is age, when you finish a book you don’t need to go back through the pages again,” she says, with just a hint of sadness. “That’s it, that’s the story. I have made it as long and as beautiful as I could. Now I want to end it beautifully.”

Her future, after December, is not planned. She may return to the theatre in some way. She may involve herself more in environmental campaigning. She may do nothing at her homes in Italy and Switzerland. “I wait and see. I like nature, I like animals. I also like peace, to be in the middle of nowhere with my dogs, working the soil to plant my seeds, taking care of my olive trees. I do love that and maybe I will be happy with that. I don’t know.”

Now she has simply to build enough stamina to take her through a long evening, in which she will perform three out of the four works. “It’s a huge discipline to say OK, I need to go through this over and over again. And if you are dying, you know that tomorrow you won’t die so much. It is painful but it gets easier. It is like banging yourself on the head until you don’t feel the pain any more. It’s the only way.” A huge grin breaks across her face.

Ten to six: Guillem with Nureyev in the Seychelles, 1986

For all the bruises, it is clear that Sylvie Guillem is enjoying herself. As she tours the world, to Europe, China, Japan, America, she is letting everyone say goodbye to her singular talent. The concluding work on the programme is “Bye”, a solo to Beethoven’s final piano sonata, choreographed by Mats Ek, who is also retiring this year. It is a work that combines joy and sorrow, a reach for freedom with a kind of rueful acceptance that one day it will end. Guillem fills it with drama, nuance and affection, loading each gesture with meaning. “It was just a given”, she says, “that this would be the last piece.”

Ek, who has made three works for her, calls her “a blue flame”. It is the right image for both the woman and the dancer, cool and passionate simultaneously. She burns with integrity, with a pure vision of who she is and what she can achieve. Hers has been one of the defining careers of dance, one that flared so brightly that it altered the landscape. When she stops dancing, the world will be a little darker.■

Sylvie Guillem: A Life in Progress Lodz International Ballet Festival, May 15th-16th; Sadler’s Wells, London, May 26th-31st; Athens & Epidaurus Festival, June 3rd-4th; touring to December 20th