Bernstein

He did everything he did at the top of it: music director of the New York Philharmonic, composer of West Side Story, and the man who explained sonata form on television to several million American children. In 1943, aged twenty-five, he stepped in for the ailing Bruno Walter at a nationally broadcast concert and was on the front page of the New York Times the next morning.

What he cared about was composing, and it was also what pained him — the serious works were long held to be lesser than the musicals. In hindsight, the tritone that runs through West Side Story, the first two notes of 'Ma-ri-a', is as solid a piece of compositional technique as anything. He was also Mahler's most important advocate and nearly single-handedly returned him to the concert repertoire.