Richard Feynman
Young Richard
Mel Feynman
Harold
Robert (as Raffi DiBlasio)
David (as Joshua Wiener)
Arline Greenbaum
Abacus Adder
Kid
Young Joan
Tutti Feynman
County Dr. #1
Mr. Greenbaum
County Nurse #1
County Dr. #2
County Nurse #2
Neighborhood Doctor
Dr. Gell-Mann
Aunt Ruth
Aunt Rose
John Wheeler (as James LeGros)
Bill Price
Family Doctor
Driver
Passenger #1
Passenger #2
Passenger #3
Gil
Gate Guard
Calculator Kid #1
Stan Ivanek
Calculator Kid #2
Calculator Kid #3
Calculator Kid #4
Garo
Rob
Chepa
Nurse Kate
Strong Fellow
Mechanic
Nurse Gracie
Sewing Girl on Train
Joan Feynman (as Kristin Dattilo Hayward)
Isadore Rabi
Henry
WWII Soldier (uncredited)