By 1947, the actress now known as Marilyn Monroe was landing bit parts in small films, and within a few years she was landing bigger parts in larger films (via IMDb). In 1953, her breakout roles came with the flicks "Gentlemen Prefer Blondes" and "How To Marry A Millionaire," solidifying her as a bona fide Hollywood star still under contract with 20th Century Fox. It was defying that contract with a determination to stop playing blonde bimbo roles that really paved the way for Monroe, according to Marie Claire.
Monroe did what few female stars were able to do at the time. She told the studio she was under contract with that she would stop working, and then formed her own company called Marilyn Monroe Productions. She moved to New York to study acting and ignored lawsuit after lawsuit from 20th Century Fox. By 1955, the studio relented to Monroe's demands and offered her $100,000 per film, as well as creative control. In fact, she paved the way for others to start their own production companies, as well, which seemed to lead to the end of Hollywood's studio system (via Marie Claire).
