Otto Nossan Klemperer (14 May 1885 – 6 July 1973) was a German-born conductor and composer. He is widely regarded as one of the leading conductors of the 20th century.
Otto Klemperer was born in Breslau, Silesia Province, then in Germany (now Wrocław, Poland), as a son of Nathan Klemperer, a native of Prague, Bohemia (today's Czech Republic). His parents were Jewish. Klemperer studied music first at the Hoch Conservatory in Frankfurt, and later at the Stern Conservatory in Berlin under James Kwast and Hans Pfitzner. He followed Kwast to three institutions and credited him with the whole basis of his musical development. In 1905, he met Gustav Mahler while conducting the off-stage brass at a performance of Mahler's Symphony No. 2, Resurrection. He also made a piano reduction of the second symphony. The two men became friends, and Klemperer became conductor at the German Opera in Prague in 1907 on Mahler's recommendation. Mahler wrote a short testimonial, recommending Klemperer, on a small card which Klemperer kept for the rest of his life. Later, in 1910, Klemperer assisted Mahler in the premiere of his Symphony No. 8, Symphony of a Thousand.