This film was originally planned as a vehicle for Rex Harrison. After some false starts, it was eventually decided that Jack Hawkins should have an American co-star to play the role of "Fraser"; this necessitated extensive script re-writing. Cliff Robertson agreed to play the part, but insisted on an American writer to do the rewrite. He called in the novelist William Goldman, whom he had previously hired to write a film script based on the science-fiction novel "Flowers For Algernon", by Daniel Keyes. Goldman got his first film writing credit on "Masquerade", but when Robertson finally got to make the "Flowers For Algernon" film (renamed "Charly", in 1968), another screenplay, by Stirling Silliphant, was used.