If imitation is the highest form of flattery, than simply the many imitations of Chaplin indicate the great influence he has had on American film and acting. Chaplin's "tramp" character has been imitated hundreds of times in all kinds of film and performance roles including plays and even opera. His life has been portrayed in film, he has been imitated in commercials, shown up on a postage stamp, etc.
Several of his productions are considered landmarks including "City Lights" and "Modern Times," and his scores and other movies played a large role in lnfluencing many films long after his career ended and even long after his death.
Chaplin was also one of few public figures to be so popular as to be able to maintain his career while also taking relatively unpopular political positions including opposition to World War I and his disdainful view of capitalism.