In the early 20th century, the 'Star System' in Hollywood refers to a practice of building and promoting actors as major stars. Studios would sign actors to long-term contracts. The actors would undergo extensive training and the studio would have the contractual right to manage their career and image. Prior to the Star System, Hollywood actors were significantly less famous.
Famous stars who were a part of the Star System include Marilyn Monroe, Greta Garbo and Clark Gable.