Klaatu
Klaatu is a humanoid visitor from an alien civilization which has learned how to live without stupidity as well as live together in peaceful co-existence. This idealistic utopia has been achieved through the creation of a police force of powerful robots who are capable of devastating any planet that does not agree to control and restrain aggression. He has arrived on earth to deliver the message that they will be accepted into their federation if they agree to the terms. If not, they must face the consequences.
Gort
Gort is one of robot policemen that accompanies Klaatu to earth. He tall, metal and with a death ray that comes out from beneath a visor. He stands at the ready to destroy mankind should anything happen to Klaatu. The only failsafe to prevent this destruction is a cryptic phrase that Klaatu passes along to a human woman: “Klaatu barada nikto.”
Helen Benson
Helen is a young widow with a son who lives in the boarding house in which Klaatu stays while observing the human race incognito under the named Mr. Carpenter. Helen becomes close with Mr. Carpenter even as her son Bobby insists that he saw Mr. Carpenter enter the flying saucer after Gort knocks a couple of soldiers unconscious. Helen’s boyfriend Tom does not take kindly to this turn of events.
Bobby Benson
While watching out for Bobby while Helen is away, the boy and Mr. Carpenter visit the Lincoln Memorial. Klaatu says he would have liked to have met him and asks Bobby if there is anyone alive who is considered as great. Bobby tells him about Professor Barnhart who is a character based on Albert Einstein.
Prof. Barnhart
Eventually Klaatu succeeds in meeting Barnhart and he informs him of the real motivation for his arrival on earth. The representatives of the other alien civilizations have become alarmed by the recent development of atomic bombs and the threat it represents to the anti-aggression pact they have agreed to which has ensure peace for all. Klaatu tells the Professor that if mankind ignores his warning, it will face extinction.
Tom Stevens
Tom is dubious about Bobby’s story of seeing Mr. Carpenter enter the space ship until he steals a diamond from the boarder’s room and has it examined by a jeweler. When he reports his suspicions to the authorities, Helen rejects him and sides with Carpenter, eventually discovering he is Klaatu and being entrusted with the failsafe phrase.
