Nolan had long desired to make a film about Oppenheimer, even prior to reading American Prometheus. In 2019, towards the end of production on Nolan's science-fiction film Tenet (2020), star Robert Pattinson gave him a book of Oppenheimer's speeches. According to Nolan, the speeches showed Oppenheimer "wrestling with the implications... of what's happened and what [he's] done". Nolan wanted to depict "what it would have been like to be Oppenheimer in those moments", in contrast to Tenet, which employs time travel to curb a potential weapon of mass destruction.