Since 1933, the orchestra has not had one main conductor, but instead it has many guest conductors who have stayed for short periods. These have included a great many of the world's best known conductors, including Richard Strauss, Arturo Toscanini, Hans Knappertsbusch, Wilhelm Furtwängler, Karl Böhm, John Barbirolli, Herbert von Karajan, Carlo Maria Giulini, Georg Solti, Erich Kleiber, James Levine, Zubin Mehta, Carlos Kleiber, Leonard Bernstein, Claudio Abbado, Riccardo Muti, Nikolaus Harnoncourt, Pierre Boulez, Lorin Maazel, Mariss Jansons, Daniel Barenboim and Valery Gergiev. Three conductors, however, gave many concerts with the orchestra during the period after World War II: Karajan and Böhm, who were made honorary conductors, and Bernstein, who was made an honorary member of the orchestra.