 In September 2013, Vaughn cast Sophie Cookson for the female lead, preferring a newcomer over more obvious candidates like Emma Watson and Bella Heathcote.Mark Hamill was cast as Professor James Arnold, a reference to his character in the source comic book being named "Mark Hamill".Millar and Vaughn stated that a sequel was possible if the first film performs well at the box office, and Vaughn expressed interest in directing the sequel.