American operatic baritone known for his work in operas of Ruggero Leoncavallo and Giacomo Puccini.

The son of Russian Jewish immigrants, Warren first studied music at the Greenwich House Music School in New York City and sang in the chorus at Radio City Music Hall from 1935 to 1938. In 1938, after vocal study with Sidney Dietch, he entered the Metropolitan Opera radio auditions and won both a contract and a scholarship to study in Milan. He first appeared at the Metropolitan in 1938 in a concert of operatic excerpts and made his operatic debut—as Paolo in Giuseppi Verdi's Simon Boccanegra at the Metropolitan—in 1939.

In addition to an extensive American career, Warren toured South America, Canada, Italy, and the Soviet Union. His greatest successes were in the operas of Verdi, as Tonio in Leoncavallo's Pagliacci, and as Scarpia in Puccini's Tosca. He made numerous appearances on radio and film and made many recordings. He died on stage at the Metropolitan during a performance of Verdi's La forza del destino.