Complex sentence: The film's exposition explains that Roth had worked diligently for the Corleone Family during Prohibition, and was a close friend and ally of Moe Greene (Alex Rocco), whom he treated like a a little brother when the two were growing up in New York.
Split into simpler sentences: The film's exposition explains that Roth had worked diligently for the Corleone Family during Prohibition, and was a close friend and ally of Moe Greene (Alex Rocco). Who he treated like a a little brother when the two were growing up in New York.