Michael Rennie

Character: Klaatu, alias Mr. Carpenter

Patricia Neal

Character: Helen Benson

Billy Gray

Character: Bobby Benson

Sam Jaffe

Character: Prof. Jacob Barnhardt

Hugh Marlowe

Character: Tom Stevens

Lock Martin

Character: Gort

Freeman Lusk

Character: General Cutler

Edith Evanson

Character: Mrs. Crockett, landlady

Frank Conroy

Character: Mr. Harley, Secretary to the President

Frances Bavier

Character: Mrs. Barley, boarder

John Brown

Character: George Barley, boarder

Olan Soule

Character: Mr. Krull, boarder

Marjorie Crossland

Character: Hilda, Barnhart's secretary

Elmer Davis

Character: Elmer Davis

H.V. Kaltenborn

Character: H. V. Kaltenborn

Drew Pearson

Character: Drew Pearson

Gabriel Heatter

Character: Gabriel Heatter (voice)

Harry Lauter

Character: Lieutenant in Charge of Landing Site

James Doyle

Character: Army Dr. White

Larry Dobkin

Character: Balding Army Doctor

Robert Osterloh

Character: Army Examining Doctor

Glenn Hardy

Character: Radio Interviewer at Landing Site

Tyler McVey

Character: Brady

House Peters Jr.

Character: M.P. Captain at Barnhardt's

George Lynn

Character: Conference Colonel Ryder

Dorothy Neumann

Character: Margaret, Tom's secretary

Wheaton Chambers

Character: Mr. Bleeker, jeweller

Carleton Young

Character: Zone Five Lieutenant Colonel

Harry Harvey

Character: The Cab Driver

Sammy Ogg

Character: Sammy, boy witness

Bess Flowers

Character: Lady Outside Jewelry Store

James Seay

Character: Government Man

Grady Galloway

Character: Radar Operator

Hassan Khayyam

Character: Indian Newscaster

John Barton

Character: British Newscaster

Stuart Whitman

Character: Sentry (scene deleted)

Rama Bai

Character: Scientific Delegate

John Burton

Character: British Radio Announcer

Bill Welsh

Character: Radio Announcer (voice)

Guy Williams

Character: Radio Operator (uncredited)