- Marvin L. Goldberger
- Self - Physicist
- Priscilla McMillan
- Self - Author, 'The Ruin of J. Robert Oppenheimer'
- Richard Rhodes
- Self - Author, 'The Making of the Atomic Bomb'
- Martin Sherwin
- Self - Professor Emeritus, Princeton University
- Herbert York
- Self - Physicist
- Freeman Dyson
- Self - Physicist
- Robert Christy
- Self - Physicist
- Roy J. Glauber
- Self - Physicist
- Harold Agnew
- Self - Physicist
- Jeremy Bernstein
- Self - Author, 'Oppenheimer: Portrait of an Enigma'
- David Strathairn
- J. R. Oppenheimer
- Daniel Gerroll
- Colonel Pash
- Michael Stuhlbarg
- Edward Teller
- Boyd Gaines
- The Voice of Chairman Gray
- Ellen Katz
- The Stenographer
- Campbell Scott
- Self - Narrator
- Albert Einstein
- Self
- Dwight D. Eisenhower
- Self
- Leslie Groves
- Self
- J. Edgar Hoover
- Self
- Lyndon B. Johnson
- Self
- Joseph McCarthy
- Self
- J. Robert Oppenheimer
- Self
- Joseph Stalin
- Self
- Lewis Strauss
- Self
- Edward Teller
- Self
- Harry S. Truman
- Self
