 Singers who have been associated with the company include Geraint Evans , Thomas Allen , Anne Evans , and <unk> Terfel . Guest artists from other countries have included Joan Hammond , Tito <unk> and Elisabeth <unk> . Among the <unk> have been Sir Charles Mackerras , Reginald Goodall , James Levine and Pierre Boulez . The company has been led since 2011 by David Pountney as chief executive and artistic director . 
