The Great Dictator is a 1940 American political satire comedy-drama film written, directed, produced, scored by and starring British comedian Charlie Chaplin, following the tradition of many of his other films. Having been the only Hollywood filmmaker to continue to make silent films well into the period of sound films, this was Chaplin's first true sound film.
When it came out the film was the most popular sound film Chaplin had ever made. 
It was his first sound film and when it came out it was the only one he'd ever made  so it had to have been the most popular example. 