When he met these politicians in the ’90s, Gergiev was the celebrity. “No one knew these people, and I was so famous already,” he told me. Once in power, Putin and his associates shaped a Russia that diverged darkly from any youthful liberal visions. Gergiev said that his ongoing relationships with these men are based on shared cultural viewpoints. “It is not personal, this in return for that,” he said. “They understand the importance of the Mariinsky.”

GERGIEV’S ABILITY TO LEAD MUST have inspired his piano teacher in Vladikavkaz, the North Ossetian city where he grew up, to suggest that he study conducting. She introduced him to Anatoly Briskin, a conductor, who gave him lessons, although Gergiev was more interested in playing soccer. Then everything turned more serious. His father, an officer in the Red Army, died of a stroke when Gergiev was 14. “That was so far the single saddest day of my life, when this happened,” he told me. “I suddenly realized my life was completely different.” He began playing the piano more. “I didn’t feel I wanted to be with a lot of people, maybe,” he said. Briskin told him that if he wanted to pursue conducting, the only path was to study in Leningrad with Briskin’s own teacher, Ilya Musin, who had a long, legendary career of training young conductors. Gergiev took the advice. From Musin, he imbibed an attitude as well as a technique. “He tried to teach everyone to find a reason for joy in making music,” he said. While still a student, Gergiev in 1977 won the Herbert von Karajan conducting prize. Karajan asked Gergiev to come work with him in West Berlin, but the Soviet authorities wouldn’t permit it. Instead, he stayed in Leningrad, where he became an assistant conductor at the Kirov.

As a leader, Gergiev’s core constituency is his family. His older sister, Larissa, runs the academy for young singers at the Mariinsky, and the husband of his younger sister works at the theater as well. He has installed his mother, along with his two sisters and their families, in apartments in the St. Petersburg waterfront building where he lives with his wife, Natalia Dzebisova — an Ossetian who is 27 years his junior and whom he met when she was a student at the same music school that he attended as a boy, an institution that had been renamed for him by the time she enrolled there. (They have three children.) His devotion in particular to his elderly mother is unstinting. In his three-story pink stucco dacha, large and comfortable but hardly opulent, which he built a year and a half ago in a wooded, suburban district near the Baltic Sea, he included, in addition to her bedroom suite, a glass elevator that allows her to get around easily. But Gergiev’s concept of family extends beyond blood ties. When the financier and munificent music patron Alberto Vilar, who had generously supported the Mariinsky, was arrested in 2005 on fraud charges, other opera companies that had benefited from his largess turned their backs on him. Gergiev personally sent him $500,000 to post bail.

Gergiev’s loyal relationships with wealthy friends and government officials keep the Mariin­sky afloat. For the past eight years, he has been pushing to build a Mariinsky II opera house, budgeted at about $500 million, to complement the jewel-box auditorium within the pale green, 19th-century Mariinsky Theater. By meeting with Putin and two cabinet ministers, he received approval for the expansion. Afterward, an informal competition in 2001 and a high-profile juried competition in 2003 each selected a cutting-edge foreign architect: first, an American, Eric Owen Moss, and then a Frenchman, Dominique Perrault. Both Moss’s iceberg of glass and blue granite and Perrault’s glass-and-gold snowflake geometry provoked outraged squawks in conservative St. Petersburg. Both died on the drawing board. Gergiev then resolved to select the architect himself and found one: Jack Diamond, designer of the Toronto opera house, a Modernist glass box that Gergiev says is superbly functional. “Jack Diamond is a practical man,” he told me. He sensed the climate wasn’t right for a project like Moss’s or Perrault’s. “Although it looks very good on paper, at a time when people are worried about their jobs and children, you don’t go for extravaganza,” he said. But he needs top-level authorization to dispense with competitions and start over right away with a new architect.

We were speaking in a hotel cafe in Moscow early last month when an assistant came up and handed him a cellphone. It was Elvira Nabiullina, the minister of economic development and trade, calling to say that she had talked to President Medvedev on his behalf. Gergiev thanked her.

“People are worried,” he told me afterward. “Let’s be honest, it’s a little bit smaller people in the picture, but I know the Canadian will do the job, and I take responsibility. Some people don’t want to be blamed. If anything goes wrong, everyone wants to be sure that I will be the one guilty.”

WHEN GERGIEV LEADS AN ORCHESTRA , his left hand flutters, as if receiving spectral transmissions, and occasionally, it jerks up to push his thinning, lank gray hair out of his eyes. In his right hand, he sometimes holds a small stick (once I saw him use a toothpick), but more often, nothing. The right hand indicates entrances and tempo, which, even for professional musicians, can be hard to read. Julia Broido, a musicologist at the St. Petersburg conservatory that Gergiev attended, told me that adulatory young conducting students comically imitate the fluttering hand, “but it is a kind of magic, and it only works for Gergiev.” The alchemy is not proceeding from the hands. Andrew Marriner, who is the principal clarinetist for the L.S.O., said, “Everything happens here,” and traced from the eyes to the mouth. Gergiev’s large, protruding eyes beneath bushy arched eyebrows are extraordinarily expressive, and his face registers an emotional range that any actor would envy — from nodding, encouraging confidence to wooing, romantic yearning, from heedless rapture to the darkest scowl. When the pace of the music picks up, his whole body throbs. During a crescendo, he may pump his arms back and forth, as if he were about to dive into a pool, and he will jump up and down a couple of times. He doesn’t stand on a box, perhaps because he would fall off and break his neck, or maybe for the same reason that he doesn’t wave a big stick: he needs no props to enhance his authority.