When the company was formed, its policy was to perform all works in English, but since the late 1950s most operas have been performed in their original language. From the outset, performers have comprised a mixture of British and Commonwealth singers and international guest stars, but fostering the careers of singers from within the company was a consistent policy of the early years. Among the many guest performers have been Maria Callas, Plácido Domingo, Kirsten Flagstad, Hans Hotter, Birgit Nilsson, Luciano Pavarotti and Elisabeth Schwarzkopf.