Complex sentence: Marx used an Italian accent for his on-stage character; stereotyped ethnic characters were common with Vaudeville comedians, and all the Marx brothers sometimes performed "dialect characters" early in their careers, but Chico was the only one to continue this into their films.
Split into simpler sentences: Marx used an Italian accent for his on-stage character; stereotyped ethnic characters were common with Vaudeville comedians. All the Marx brothers at some point in their careers performed "dialect characters," but Chico was the only one to continue this into their films.