Stan Ulam
Françoise
Jack Calkin
Edward Teller
Johnny von Neumann
Robert Oppenheimer
Klaus Fuchs
Adam Ulam
Norris Bradbury
Carlos
George Dyson
Mici Teller
Irene
Jacky (as Anne-Catrin Märzke)
Henry Hitchens
Molly
Mathematician at Los Alamos
Stefania Ulam
G.D. Birkhof
Ruth (as Aneliese Kelly)
Stefania Ulam (voice)
Stefania Look-Alike (uncredited)
Scientist (uncredited)