Paul Newman

Gen. Leslie R. Groves

Dwight Schultz

J. Robert Oppenheimer

Bonnie Bedelia

Kitty Oppenheimer

John Cusack

Michael Merriman

Laura Dern

Kathleen Robinson

Ron Frazier

Peter de Silva

John C. McGinley

Richard Schoenfield

Natasha Richardson

Jean Tatlock

Ron Vawter

Jamie Latrobe

Michael Brockman

William "Deke" Parsons

Del Close

Dr. Kenneth Whiteside

John Considine

Robert Tuckson

Allan Corduner

Franz Goethe

Joe D'Angerio

Seth Neddermeyer

Jon DeVries

Johnny Mount

James Eckhouse

Robert Harper

Todd Field

Robert Wilson

Mary Pat Gleason

Dora Welsh

Clark Gregg

Douglas Panton

Péter Halász

George Kistiakowsky

Gerald Hiken

Leo Szilard

Arthur Holden

Oakridge Doctor

Ed Lauter

Whitney Ashbridge

Donald MacKechnie

James Tuck

Madison Mason

Boris Pash

Krzysztof Pieczyński

Otto Frisch

Don Pugsley

Bronston

Logan Ramsey

Brehon Somervell

Fred Thompson

Melrose Hayden Barry

Jim True-Frost

Donald Hornig

Barry Yourgrau

Edward Teller

Marek Alboszta

Scientist

Steven Baigelman

Dr. Avenell

Frank Benettieri Jr.

Messenger

Roger Cubicciotti

Frank Oppenheimer

Franco Cutietta

Enrico Fermi

Robert Peter Gale

Dr. Louis Hempelman

Wesley Harrison

Peter Oppenheimer

Brent Harrison

Peter Oppenheimer

Tom McFarlane

Scientist

David C. Parnes

Raincoat Man

Allen Poirson

Harold McDonald

David Politzer

Robert Serber

Bill Rubenstein

Times Reporter

Ken Strausbaugh

Observation Officer

Walter Sullivan

Henry Stimson

Brian Wandell

Dennis Talmudge

John Williams

Mack Stoddard

Walker Edmiston

(voice)

Matthew Faison

(voice)

Stan Jones

(voice)

Alan Oppenheimer

(voice)