Oppenheimer marks the sixth collaboration between Nolan and Cillian Murphy, and the first starring Murphy as the lead. To prepare for the role, Murphy read extensively on Oppenheimer's life and was inspired by David Bowie 's appearance in the 1970s. Nolan called Murphy one day to ask him to play the part, and Murphy enthusiastically accepted, excited to play a lead role in a Nolan film. Afterward, Nolan flew to Dublin to meet with Murphy, who read the script in Nolan's hotel room. Murphy lost an undisclosed amount of weight for the role in order to better match the real-life Oppenheimer's gaunt appearance. Nolan also set up a phone call between Murphy and Nobel laureate Kip Thorne, who had previously worked with Nolan on Interstellar (2014). As a graduate student, Thorne had attended some of Oppenheimer's seminars, and explained to Murphy his experience with Oppenheimer's gift for facilitating group discussions of difficult scientific concepts.