Upon hearing one particular baritone voice during the Metropolitan Opera auditions of 1938, conductor Wilfrid Pelletier rushed into the auditorium to check that someone was not substituting a recording of an established singer. Instead, he discovered Leonard Warren: a young man in his 20s who had seen just one opera before, whose repertoire was only five areas, and whose stage experience to that point consisted of a high school play. His natural voice must have been amazing, because he was hired on the spot, and sent to Italy for a crash course in opera singing. His voice was perfectly suited to Verdi's baritone roles, and thus he became a great opera star and a mainstay at the Met.
According to Peter Davis in The American Opera Singer, he had a "deluxe, quintessentially Metropolitan Opera sound". He also had a quintessentially dramatic death:
"Indeed, the most dramatic moment of Warren’s life came on the very last night of it, during a performance of La Forza del Destino... The baritone was about to launch the rousing cabaletta to Don Carlo’s aria, which begins 'Morir, tremenda cosa' (to die, a momentous thing), when he pitched face-forward to the floor. A few minutes later he was pronounced dead of a massive cerebral vascular hemorrhage, and the rest of the performance was canceled. Warren was only forty-eight."
There are several clips of Warren on YouTube; I've selected the Toreador song from Carmen to link to here, as it is performed in concert and you see Warren as himself, without makeup. Enjoy!
Sources: Wikipedia, The American Opera Singer