Complex sentence: Damrosch was best known as a conductor of Richard Wagner and was also a pioneer in the performance of music on the radio, and as such became one of the chief popularizers of classical music in the United States.
Split into simpler sentences: Damrosch was best known as a conductor of Richard Wagner. He was also a pioneer in the performance of music on the radio, and as such became one of the chief popularizers of classical music in the United States.