To build his character, Day-Lewis started with the voice. Anderson sent him recordings from the late 19th century to 1927 and a copy of the 1948 film "The Treasure of the Sierra Madre", including documentaries on its director, John Huston, an important influence on Anderson's film. According to Anderson, he was inspired by the fact that "Sierra Madre" is "about greed and ambition and paranoia and looking at the worst parts of yourself." While writing the script, he would put the film on before he went to bed at night. To research for the role, Day-Lewis read letters from laborers and studied photographs from the time period. He also read up on oil tycoon Edward Doheny, upon whom Sinclair's book is loosely based.