Vasiliev Joins American Ballet Theater as Principal Dancer American Ballet Theater has recruited Ivan Vasiliev as a principal dancer, and will cast him during next year's season at the Metropolitan Opera and on tours, the company said on Monday. Mr. Vasiliev and the ballerina Natalia Osipova created a stir nearly a year ago when they announced they were leaving Moscow's Bolshoi Ballet for the Mikhailovsky Theater in St. Petersburg. Mr. Vasiliev, who was born in 1989 in Vladivostok, Russia, made his debut at the Bolshoi in 2006 as Basilio in "Don Quixote" and made guest appearances at Ballet Theater last year. His roles with the company included Solor in "La Bayadère," Franz in "Coppélia" and Ali in "Le Corsaire."