Dynamic, dictatorial, with no time for a private life - that's what audiences world-wide know of this great Russian conductor. Yet he has a daughter he refuses to talk about and this month he married an unknown musician aged 19. John O'Mahony on the complex maestro of the Mariinsky

It's high-altitude early morning on a rickety old Tupolov flying out of St Petersburg and Valery Gergiev is curled up on a seat by the window, sleeping like a swarthy, stubble-chinned baby. There had been two abortive attempts to secure an audience with the man they call "the busiest conductor in the world", once in the Rotterdam Holiday Inn at 3am, when he practically keeled over in mid-sentence from sheer exhaustion, and again in London's Waldorf hotel, when I'd been triple-booked with another journalist and Peter Katona of the Royal Opera House. Now this was to have been our big date.

"On the plane there'll be no-one to distract him," his personal assistant, Alisa, assured me, "The mobile phone will be switched off, there'll be no calls from agents, no other journalists. He'll be all yours." Now, she too is fast asleep, snoring gently on a seat behind me. And scattered all around the cabin is the entire Kirov orchestra and company, due to perform Tchaikovsky's Mazeppa that night in Glasgow, slumped insensate against headrests, sleeping off the heady, hectic regime of the previous week's performances.

So, the only conscious human being on this charter flight apart from the crew, I continue doodling in my notebook, anxiously contemplating the dark, rugged features of the sleeping maestro. A half-hour slips by, an hour, then two. Only as the stewardesses begin preparing for our descent do the dark eyes suddenly open, fixing me in a terrifying, gimlet-edged glare.

Without so much as a flicker of hesitation, he beckons me over: "I suppose it can't wait any longer," he growls, initiating a rambling monologue that would continue uninterrupted through landing, disembarkation, passport control, customs and out into the cool, grey summer light.

Valery Gergiev is probably the most profoundly complex and contradictory man I have encountered. A chaotic human whirlwind of disorganisational uproar who suffers from an almost pathological lack of punctuality, he is also the widely revered "managerial genius" behind the current phenomenal success of St Petersburg's Mariinsky/Kirov theatre of ballet and opera, over which he has reigned as principal conductor since 1988. A man, his sister testifies, who "cannot cook, wash his clothes or do any kind of practical housework," he has under his care a company of 80 singers, 200 dancers, 180 musicians, 120 chorus members and hundreds more technical and administrative staff, all entirely dependent on his ability to keep the theatre afloat in the uncertain financial waters of post-soviet Russia.

In the corridors of the Mariinsky, he is a stern and demanding tsar, his name spoken by employees almost in hushed tones. When younger singers are asked about their working relationship with him, they simply whisper: "He is the maestro'.' On tour, however, he can come across as just one of the gang. A schmooze session for wealthy patrons on a cruise ship in Rotterdam harbour disintegrated into a raucous early-hour operatic sing-along with the tipsy Mariinsky troupe, accompanied, in between spells of barking into a mobile phone, by a bleary-eyed Valery Gergiev on piano: "Here's one called Podmoskoveniye Vechera ," he slurred, slender fingers deftly picking out the notes of this sentimental Russian classic, "It's one of the most beautiful melodies ever written."

At 6 foot, stocky and athletic, with a handsome, rough-hewn physiognomy which has been described as "diabolic", Gergiev cuts an imposing figure. For the most part though, he is painfully gentle, his gravelly voice in rehearsals often barely audible. The headlong tonal swings and crushing musical contrasts that characterise his work are prised from the score with just a few, low-key, incisive words or a typically elliptical comment: "This opera is unplayable, unshapeable and unsingable," he told the Rotterdam Philharmonic during rehearsals for Berlioz's Benvenuto Cellini, "right, I'll see you all at 7 o' clock."

Now one of the world's most sought-after conductors, and regularly compared to the legendary Yevgeny Mravinksy, Gergiev has positions in Rotterdam and at the Metropolitan opera in New York, where the post of principal guest conductor was created specifically for him. But despite his personal wealth, he seems to expend absolutely no effort on presentation, wandering around in a ratty, green tweed jacket and lived-in chinos, his hair growing increasingly lank with every capital city stopover. Sometimes, however, there are flashes of preening vanity: "Valery is very worried about his appearance," cooed one of his helpers continually, never explaining why he didn't simply think of taking a shower.

He professes to have no time for an intimate private life and, at the age of 46, still lives with his mother. And yet he beams out a grainy sexual force, while his conducting trembles with a feral mag netism greatly prized in the drab, sparsely populated post-Karajan, post-Solti, post-Bernstein world of modern super-conductors. A committed bachelor, who many felt would never sacrifice his career to the emotional demands of marriage, he suddenly, and without warning, shocked the Russian music world by marrying an unknown 19-year-old musician two weeks ago at a traditional ceremony in his home town of Vladikavkaz, in the Caucasus state of North Ossetia-Alana.

Charismatic, capable of endlessly entertaining (and wrangling money out of) hordes of prissy millionaires, Gergiev is also obsessively secretive to the point of hiding even the most basic facts of his life from close family members: "Don't talk to too many people," he commanded towards the end of my search for those who could talk openly and honestly about him. "If you talk to too many people, I won't talk to you again."

Only at one point do all these different, irreconcilable images converge. When he steps onto the podium, preferably facing a turbulent score by Stravinsky, Shostakovich or his beloved Prokofiev, it is possible to see flashes of the boyish playfulness, bounding enthusiasm, self absorption, fiendish concentration, even the slovenliness; it's all there, overlapping, disappearing, resurfacing.

Generally dispensing with a baton, he often seems to be ripping the music out of the orchestra, stabbing violently at the strings, lifting the brass out of their seats, his whole body shuddering back and forth with each crescendo and diminuendo. At times, with his features frozen in painful ecstasy, he appears almost saintly. At others , when he bears down violently on the music, his expression has often been described as demonic. "Do you think Bernstein was not demonic?" he asks, "do you think Karajan was not demonic? Yes, a conductor has to be demonic if the music he conducts demands it - an angel if the music demands it. "

It seems perfectly natural, then, that there should be two starkly contradictory versions of his biography. The "official" version is typified by a slim soviet hagiography brought out in 1989, after he became principal conductor of the Mariinsky: "The greatest musical quality and personal quality attributed to Valery," it concludes after reams of turgid panegyric, "is his ability to rapidly attain perfection, his self-control and his continual desire to raise himself to the highest levels of mastery."

Even now, a decade into cultural liberalisation, it's difficult to extract anything more insightful from the current crop of Mariinsky singers and musicians, or from many of Gergiev's friends, associates and family members, most of whom spout paeans to the maestro's "heavenly gift", "great warmth" and "great strength of will".

Yet, no matter how bland this may seem, there really are areas of his talent and character where only superlatives apply, not least his ferocious work ethic. On a single day, he is said to have conducted rehearsals with three different major European orchestras, jetting between Rotterdam, Cologne and Munich. The Mariinsky orchestra can regularly be found in venues around the world frantically rehearsing new works, often substituted by the maestro at the last moment, the violinists giving each other back-massages like a bunch of footballers in extra time.

"When he's not abroad, he works with the theatre for 18 hours a day," says Yuri Svartzkopf, the Mariinsky managing director. "He leaves at 3 or 4 in the morning, sleeps a little and then comes back." His achievements with the Mariinsky/Kirov, which he has built into one of the world's greatest companies, are correspondingly superhuman. Last season, even after Russia's banking meltdown swallowed up $2.8m of general company funds which had been earmarked to support new productions, the theatre still managed to pump out five new premieres, (one was the norm during the Soviet period) including a new Lohengrin and a startling reinterpretation of Prokofiev's soviet opera Semyon Kotko. The Kirov Ballet is enjoying enormous success and recently dazzled New York with a historically authentic production of Petipa's original Sleeping Beauty.

His annual Stars of the White Nights Festival now forms the backbone of the St Petersburg cultural calendar and, next July, he plans to overwhelm London with a month-long Mariinsky mini-season at Covent Garden.

"If it hadn't been for Gergiev, the Mariinsky theatre would have died by now," says his predecessor, Yuri Temirkanov, a giant on the St Petersburg music scene, who was principal conductor of the Mariinsky from 1976-88 and now presides over the St Petersburg Philharmonia. "Just like the Bolshoi Theatre in Moscow has died because they don't have such an organiser, administrator and general madman. Gergiev is the reason why the Mariinsky is alive."

Curiously, the contrasting "unofficial" story of Valery Gergiev is typified by another little volume, a satirical novel called Phantom Of The Opera In The City Of N', by Kirill Shevchenko, the journalist husband of Elena Prokina, the disaffected former Mariinsky singer. Aping the style of Mikhail Bulgakov, the book chronicles the exploits of Abdullah, (Gergiev's irreverent, racially-tinged nickname in the theatre.) the nauseatingly ambitious, dictatorial head of the N'sky Theatre.

Though of negligible literary merit, and containing many risible episodes, the book has been through two print runs and practically every musician, singer, dancer and admin istrative worker in the Mariinsky theatre has a copy. In spirit, the novel reflects an entirely different side of Gergiev; the control freak who, Shevchenko claims, "has total jurisdiction over everything from dispensing money during tours to deciding the bonuses of the Mariinsky drivers".

When theatre staff refer to Abdullah, they are talking about the despot who drives singers like thoroughbred horses until their voices dry up, who rehearses the orchestra for hours on end without a break until bladders fill to bursting. "I was surprised how much Kirill knew about rehearsals and the workings of the theatre," said a Mariinsky insider, "About 75% of what's written there is true."

Situated somewhere between these opposing versions, acting rather like a fulcrum, are the facts. Valery Gergiev was born in Moscow on May 2, 1953, the first and only son of Tamara Tatarkanovna and Abisal Zaurbekovich, both of Ossetian origin. His father, a military officer in the Red Army, was soon reassigned to Vladikavkaz, where the young boy grew up in an exceptionally close-knit extended family.

While Gergiev has often spoken of his background as "not typically musical", his parents made sure the family soaked up as much musical culture as provincial soviet life would allow, attending concerts by visiting stars such as Sviatoslav Richter and Mstislav Rostropovich, and sending children to study piano at the local music institute.

Gergiev's sisters testify to "a very happy, almost idyllic childhood", and conjure up pictures of an energetic, if restless, brother who preferred playing table tennis to practicing his scales. "He always seemed to be in his own world," says elder sister Larissa. "It's even possible to see it now." Though often the least prepared for exams, he would end up with the best results, convincing teachers of a mercurial, singular talent.

"Our first piano teacher started to notice," says younger sister Svetlana. "His touch on the instrument was different to ours." When Valery was 14, his father died of a heart attack, at the age of 49. "His death was the single strongest influence on my entire life," Gergiev says. "In one day I became the head of a very strong family. Before my father died I didn't know there was a problem in this world."

This calamitous shock seems somehow to have galvanised his desire to pursue a career in music, which Larissa claims surfaced immediately afterwards. A department of conducting had to be specially opened in the Vladikavkaz music college (now re-christened the Gergiev college) to accommodate the talented boy. In 1972, at the unusually early age of 19, Gergiev moved on to the Leningrad conservatory, where he won a place on the conducting course of the late Ilya Musin, whose students have also included Temirkanov, Semyon Bychkov and Sian Edwards, among others.

When I met the 95-year-old Musin in early June, just a week before his death, he had only praise for his glittering protégé, whom he rated "much higher than Solti". This brilliance, however, wasn't immediately apparent: "His conducting technique was always very particular and quite unusual. But he is very emotional and completely 'lives' the music, not caring about rules," Musin said.

Also starting at the conservatory in the same year was Marina Malkiel, with whom the 19-year-old had what was perhaps his first relationship, a stormy, on and off affair that continued until graduation: "You can imagine what it was like for a boy straight from the Caucasus," Malkiel says. Now 46, a music historian, and still very striking, she says '"He was a little wild, and in a way, quite uncivilised. Sometimes he didn't appear to know even the most basic manners. But he was highly motivated, completely fanatical and deeply in love with music. And he was always very proud and ambitious. Even then, he always said that he'd reach the level of Mravinsky. It's difficult to say which was the stronger force, his love of music or his ambition."

The intense chaos of Gergiev's scatter-gun routine, which is often now put down to the demands of running a vast theatre, was also present in the carefree youth of 19. "He's always had those traits of forgetfulness and absent-mindedness,' Malkiel says , "he never had any feeling of time."

While many student contemporaries stress his boisterous nature, those who crept closer saw a darker side: "He was always very conspiratorial and hid our relationship from his family," Malkiel says. "He's a very lonely person. If he's trying to make out that every thing is rosy and wonderful, it's basically to persuade himself. He's not a light, bright person. He's got some pain inside and he cannot laugh or have fun."

In 1977, after an impressive showing at the soviet all-union conducting contest and, that summer, at the Herbert von Karajan conductor's contest in Berlin (second positions in both, with no first awarded), Gergiev was taken on at the Kirov theatre. Despite assisting Temirkanov on Prokofiev's War And Peace, as well as successes with Manon Lescaut and Lohengrin, he counts this a "difficult period". "There were times when I thought of leaving," he says, "When I conducted very badly in a production of Trovatore, and in Don Pasquale. It was not really bad conducting, but it was nothing close to real style."

Yuri Dimitrin, an opera librettist who knew Gergiev at this time, remembers "a very patient and creative person waiting for his hour to come", a solitary young man who "never talked about his personal details and didn't appear to have much of a private life", though this was not quite the case. Some time over this period, Gergiev met a pretty young language teacher from the Leningrad conservatory named Lena Ostovich, who was to become the mother of his daughter.

While the existence of 14-year-old Natasha is an open secret in St Petersburg music circles (there are even persistent rumours of a second daughter), and various official documents quote him as being the father, Gergiev never speaks publicly about her and appears to have kept even his own family in the dark. "A daughter?" yelped his sister Larissa when I broached the subject, "I didn't know. Valery never told me anything about it."

Lena Ostovich could shed no further light on the situation and was permitted to issue only a brief "official" tribute to the maestro's "warmth" and "judgment". Why exactly he is so agonizingly secretive about the girl, who bears an uncanny resemblance to her father and is something of a piano-playing prodigy, will have to remain another of those Gergiev mysteries.

When Temirkanov moved on to the Leningrad philharmonia in 1988, the Kirov administration decided, in accordance with the modish fads of glasnost, to democratically elect his successor for the first time in the history of the theatre. Other candidates included Mariss Jansons and Dimitri Kitayenko, each of whom received a paltry 8 votes, as well as Gennady Rozhdestvensky, a goliath on the Moscow orchestra circuit, who garnered just one vote. Gergiev, who'd been endorsed by Temirkanov, won by a landslide with 285.

For the ambitious young maestro, the timing couldn't have been more perfect. The same liberating forces that propelled him into one of the USSR's most prestigious cultural posts at the obscenely youthful age of 34 were also shaking up the "meat and potatoes" Russian operatic repertoire of Tchaikovsky and Glinka. Gergiev's more "radical" projects included reviving the mammoth original five-hour version of Mussorgsky's Khovanchina, performing both the 1869 and 1872 incarnations of Boris Godunov, and reinstating Shostakovich's original Lady Macbeth Of Mtsensk alongside Katerina Izmailova, the sanitised later version.

With festivals devoted to Mussorgsky, Prokofiev and Rimsky-Korsakov, Gergiev set about like a musical archaeologist, excavating works that had been buried under decades of soviet ideological detritus. There was some resistance, but his white-hot energy, bluster and sheer audacity generally prevailed. Gergiev also set about changing the entire culture of the theatre, drenching it in his stringent work ethos. By maintaining the excellent string section and beefing up the weaker brass and woodwind with enthusiastic young players, he transformed the Kirov into one of the world's top orchestras.

He also began to forge a coherent house style: sharp, steely sopranos, rich booming basses, minimal vibrato all round. International touring, made possible at first by perestroika and then imperative by the collapse in state funding, turned most of those who rose to the Gergiev challenge into international stars. "It was a wonderful time," says Elena Prokina, an early Gergiev discovery, "all of the young singers were very much affected by his charm and magnetism, both as a musician and as a person. Our relationship with him was warm and informal: we worked as a team."

It is difficult to pinpoint when exactly this consensus began to break down into the "official" and "unofficial" credos. It probably coincided with Gergiev's consolidation of power: "It wasn't a one-step process," says Malkiel, whom he invited to become head of the Kirov's literature department, "and it wasn't particularly easy for him. His predecessor was not just a nobody, but Temirkanov, who will always be remembered in that theatre.

"I think the transformation began around the time of the Mussorgsky festival in 1989. Soon, he had accumulated enough power to control the entire theatre." More authority in the driven, disordered maestro's hands, it's claimed, translated into frantic working conditions, exhausting routines and arbitrary treatment of members of the company. The endless rehearsals began to challenge, musicians say, the physical limits of the orchestra: "There was a running joke during rehearsals which is still popular," says one occasional player. "Before taking our seats in the pit, the cry would go up: 'Diapers in place, everybody?"' Those who dissented, or even simply had the temerity to ask for a break, could find themselves consigned to the professional gulag.

The maestro also began to make hazardous impositions on singers. Elena Prokina recounts how she was given 24 hours to prepare for the lead in Prince Igor, and still shudders at the "disaster" of La Traviata when she had just three weeks to learn the role. "I felt as if my voice was being dissipated," she says. Straying too far from the Mariinsky fold risked Gergiev's extreme displeasure, as Prokina herself discovered in 1992 when she flew to Vienna mid-season to attend an audition. Though she maintains that she always intended to return in time for a performance of The Gambler, in which she was singing the lead, the fury of the maestro kept her away and eventually forced her decision to quit.

"I pulled myself together," she says of the aftermath, "only to discover that not a single Mariinsky pianist was willing even to acknowledge me when I greeted them in the street, let alone rehearse with me. That was when I realised for the first time that they were all afraid of something." Some time afterwards, Phantom Of The Opera appeared in bookshops around St Petersburg.

On a personal level, those close to Gergiev have also noticed marked changes since he became principal conductor: "The person I knew before and the one I see now," said one former advocate who worked at the Mariinsky for many years, "it's difficult to believe it is the same man." For the sake of his work, the maestro appears to have hacked away almost every aspect of his private life with the exception of his all-enveloping Ossetian family, now carefully transplanted from Vladikavkaz (his sister Svetlana acts as a personal assistant, Larissa runs the Mariinsky singers academy).

Many old friends have little or merely pragmatic contact with him. The director Yuri Alexandrov, an inseparable "best friend" during the early Kirov years, carefully counts himself "a colleague" now. After an association stretching back 28 years, Malkiel lost out last year as a pawn in one of the Mariinsky's Byzantine power struggles and now works at the philharmonia. "He lost all his friends along the way," she says. "He's an intelligent man. I think he understands this."

His ardent supporters would, naturally, come to completely contrasting (and equally justified) conclusions: "That's all rubbish," snorts soprano Galina Gorchakova, "Valery has never once forced any of us to work more than we want to. He gives you a choice of parts, and you can take what you want." His sisters point to his new marriage, which they hope will allow him to "pass on his great talent" and to friendships with the violinist Yuri Bashmet, pianist Alexander Toradze and Placido Domingo who praises his "enthusiasm" and "great leadership".

Some advocates acknowledge a murkier side, but are firmly behind Gergiev's objectives: "Without a doubt, Valery Gergiev is a dictator," says Yuri Svartzkopf, "He'll tell you that himself plainly and openly. But he is a creative dictator."

This is the position taken up by Gergiev himself who believes that all the sacrifices he has made have been totally justified: "You have to decide," he says, "do you want to have a private life, or do you keep this position at the Kirov? And I find it altogether too attractive - how the orchestra played for me this year, how the chorus sings, how the young singers progress . . . That is my satisfaction." Perhaps a conductor who can earn tens of thousands of dollars per performance in the west but chooses to work for most of the year in a theatre that pays him a minuscule $3 a night has a right to just a few unrealistic expectations.

"Russians do not know how to work," he says, "Stalin forced everyone to work like mad. He proved with horrible methods what could be done here. Is it the only way? I hope not. What I always say is you have to work hard, and you will live very well."

However, it is through his music that Gergiev offers the most conclusive justification of his position. The music also illuminates even the most contradictory aspects of his character and behaviour. Anyone who has sat in an auditorium wracked by his thunderous reading of Mahler's 3rd symphony, or beguiled by his masterful Parsifal, might forgive him practically anything.

As a consequence, he appears to some as a saviour whose superhuman dedication is an inspiration and an example. To others, he is ruthless and imperious, with little regard for anything but self- glorification. Angel or Devil. Whatever the music demands.

Life at a glance: Valery Gergiev.

Born: May 2, 1953, Moscow.

Education: Leningrad Conservatory, 1972-77.

Relationships: Lena Ostovich, one daughter, Natasha (now 14); married: Natalya Debisova, musi cian aged 19, Vladikavkaz, September 4, 1999.

Career: Junior conductor, Kirov Opera 1977-1988; award winner in Von Karajan conductor's competition,1977; chief conductor, Armenian Symphony Orchestra, 1981-1986; elected principal conductor, Kirov/Mariinsky Theatre,St Petersburg, 1989; guest conductor, Rotterdam Philharmonic Orchestra,1995; principal guest conductor, Metropolitan Opera, New York, 1997.

 Yuri Gergiev conducts a concert performance of Parsifal at the Royal Albert Hall on September 27. Three Rimsky-Korsakov operas recorded by Gergiev and the Kirov are to be released next month. The first is Kaschey The Immortal (Philips CD 446 704-2, price £14.99).