The film flips the novel on its head, turning a cautionary tale about foreign intervention into anticommunist advocacy of American power. In writing the script, Mankiewicz received uncredited input from CIA officer Edward Lansdale, who was often said to be the actual inspiration for the American character—called "Pyle" in the novel but unnamed in this film—played by Murphy. In fact Greene did not meet Landsdale until after completing much of the novel. According to Greene, the inspiration for the character of Pyle was Leo Hochstetter, an American serving as public affairs director for the Economic Aid Mission in Indochina who was assumed by the French to “belong to the CIA,” and lectured him on the “long drive back to Saigon on the necessity of finding a ‘third force in Vietnam.’”