Cillian Murphy J. Robert Oppenheimer Emily Blunt Katherine 'Kitty' Oppenheimer Matt Damon Gen. Leslie Groves Jr. Robert Downey Jr. Lewis Strauss Florence Pugh Jean Tatlock Benny Safdie Edward Teller Michael Angarano Robert Serber Josh Hartnett Ernest Lawrence Rami Malek David Hill Kenneth Branagh Niels Bohr Dane DeHaan Kenneth Nichols Dylan Arnold Frank Oppenheimer David Krumholtz Isidor Isaac Rabi Alden Ehrenreich Senate Aide Matthew Modine Vannevar Bush