The Royal Ballet is a British internationally renowned classical ballet company, based at the Royal Opera House in Covent Garden, London, England. The largest of the five major ballet companies in Great Britain, the Royal Ballet was founded in 1931 by Dame Ninette de Valois. It became the resident ballet company of the Royal Opera House in 1946, and has purpose-built facilities within these premises. It was granted a royal charter in 1956, becoming recognised as Britain's flagship ballet company. The Royal Ballet was one of the foremost ballet companies of the 20th century, and continues to be one of the world's most famous ballet companies to this day, generally noted for its artistic and creative values. The company employs approximately 100 dancers. The official associate school of the company is the Royal Ballet School, and it also has a sister company, the Birmingham Royal Ballet, which operates independently. The Prima ballerina assoluta of the Royal Ballet is the late Dame Margot Fonteyn. History Ninette de Valois, an Irish-born dancer founded the Academy of Choreographic Art, in 1926, a dance school for girls. Her intention was to form a repertory ballet company and school, leading her to collaborate with the English theatrical producer and theatre owner Lilian Baylis. Baylis owned the Old Vic and Sadler's Wells theatres and in 1925 she engaged de Valois to stage dance performances at both venues. Sadler's Wells reopened in 1931 and the Vic-Wells Ballet and Vic-Wells Ballet School were established in premises at the theatre. These would become the predecessors of today's Royal Ballet, Birmingham Royal Ballet and Royal Ballet School. Prior to her return to Britain, Ninette de Valois had been a member of the Ballets Russes, one of the most renowned and influential ballet companies of the 20th century. The company disbanded in 1929 following the death of its founder Serge Diaghilev. When de Valois formed the Vic-Wells Ballet, she employed some of the company's former stars, including Alicia Markova and Anton Dolin, who joined as Principal dancers, and Tamara Karsavina, who worked with the company as an advisor. The Founder Musical Director was the conductor and composer Constant Lambert who had considerable artistic as well as musical influence over the early years of the company. After losing the link with the Old Vic theatre, in 1939 the company was renamed Sadler's Wells Ballet and the school became Sadler's Wells Ballet School.