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 Kenneth Branagh Dane DeHaan Dylan Arnold Frank Oppenheimer David Krumholtz Isidor Isaac Rabi Alden Ehrenreich Richard Feynman Matthew Modine Vannevar Bush Gary Oldman Harry S. Truman Alex Wolff David Dastmalchian James Remar Henry Stimson