Conversation so far:
When did George M. Cohan's career take off?
George M. Cohan's first big Broadway hit in 1904 was the show Little Johnny Jones, which introduced his tunes Give My Regards to Broadway and The Yankee Doodle Boy.
Did George M. Cohan ever star in any movies?
In 1932, George M. Cohan starred in a dual role as a cold, corrupt politician and his charming, idealistic campaign double in the Hollywood musical film The Phantom President.

Question: what were his most popular works?
Self-contained rewrite: What were George M. Cohan's most popular works?