Thinnes after seeing his performance as David Vincent in the TV series The Invaders. In the Andersons' script, Ross's first name was Stewart and he was the first person on Mars. In a 2008 interview, Thinnes said of the film: "I thought [Doppelgänger] was an interesting premise, although now we know that there isn't another planet on the other side of the Sun, through our space exploration and telescopic abilities. But at that time it was conceivable, and it could have been scary". To reflect the script's characterisation of Ross as a heavy smoker, Thinnes went through numerous packets of cigarettes over the course of the production, to the detriment of his health. In September 1969, The Age reported that the actor would demand a non-smoking clause for his next film: "He smokes about two packets a day, but the perpetual lighting up of new cigarettes for continuity purposes was too much". Ian Hendry was cast as Dr John Kane, a British astrophysicist and head of the Phoenix project. In his biography, Anderson recalled that Hendry "was always drinking" and was visibly intoxicated during the filming of the Dove crash sequence: "... he was pissed as a newt, and it was as much as he could do to stagger away. Despite all that, it looked exactly as it was supposed to on screen." In the original script, Kane's first name was Philip and he had a wife called Susan. Scenes deleted from the finished film showed the character pursuing a romance with EUROSEC official Lise Hartman, played by Loni von Friedl. Ross's wife Sharon was played by Lynn Loring. The role had originally gone to Gayle Hunnicutt, who quit early in the production after falling ill. This withdrawal led to the casting of Loring, Thinnes' then wife and a star of the TV series The F.B.I. Had she remained in the role, Hunnicutt would have appeared in a nude scene, written in to distinguish Doppelgänger from the Andersons' earlier productions. In a 1968 interview in the Daily Mail, Anderson expressed a desire to change the public's perception of Century 21, saying that his company had been "typecast as makers of children's films". On rumours that the British Board of Film Censors (BBFC) would give the film an X certificate for mature content, he stated that it was Century 21's desire to "work with live artists doing subjects unsuitable for children".