Schwarzenegger took the role at the urging of his friend Reg Park, who had previously played Hercules in three films (Hercules and the Captive Women (1961), Hercules in the Haunted World (1961) & Hercules the Avenger (1965)).
To help Arnold get the role, his agent said he had years of "stage" experience, implying theater, but Schwarzenegger had only appeared on bodybuilding stages.