In March 2018, it was revealed that Taika Waititi would not only direct but also co-star in the film as an imaginary Adolf Hitler. Speaking of the context of the role, Waititi said "It's my version of. . . a lonely boy's best version of his hero, which is really his dad", referencing the fact that in the film, the protagonist, a 10-year-old boy, is desperate to join Hitler's ranks during World War II. Later that month, Scarlett Johansson joined the cast to portray the lead child's mother, who is secretly anti-Nazi. In April 2018, Sam Rockwell joined the cast to portray "a Nazi captain who runs a Hitler Youth camp". In May 2018, Rebel Wilson joined the cast to portray "a brutish instructor in the Hitler Youth Camp the young man has just been recruited to attend". Filming was also set to begin in Prague shortly thereafter. Later that month, newcomer Roman Griffin joined the cast to star as Johansson's son and New Zealander Thomasin McKenzie was cast as Elsa Korr, the Jewish girl whom Johansson hides in her home. In June 2018, Alfie Allen was cast as Finkel, the second in command to Captain Klenzendorf, and Stephen Merchant was cast as Captain Deertz, a Gestapo agent.