Peter Graves as Dr. Paul Nelson
Lee Van Cleef as Dr. Tom Anderson
Beverly Garland as Claire Anderson
Sally Fraser as Joan Nelson
Russ Bender as General James Pattick
Taggart Casey as Sheriff N.J. Shallert
Karen Kadler as Dr. Ellen Peters
Dick Miller as First Sergeant
Jonathan Haze as Corporal Manuel Ortiz
Paul Harbor as Dr. Floyd Mason
Charles B. Griffith as Dr. Pete Shelton
Thomas E. Jackson as George Haskell
It Conquered the World is an independently made 1956 American black-and-white science fiction film, produced and directed by Roger Corman, starring Peter Graves, Lee Van Cleef, Beverly Garland and Sally Fraser. The film was distributed by American International Pictures.
It Conquered the World concerns an alien creature from the planet Venus who secretly wants to take control of the Earth. The creature makes radio contact with a disillusioned human scientist, who agrees to help because the scientist believes such an alien intervention will bring peace and save a doomed humanity from itself.
Dr. Tom Anderson (Lee Van Cleef), an embittered scientist, has made contact with Zontar, a Venusian creature, while using his radio transmitter. The alien's secret motivation is to take complete control of the Earth by enslaving humanity using mind control devices; the alien claims it only wants to bring peace to our troubled world by eliminating all emotions. Anderson agrees to help the creature and even intends to allow it to assimilate his wife (Beverly Garland) and friend Dr. Nelson (Peter Graves).
Zontar then disrupts all electric power on Earth, including motor vehicles, leaving Dr. Nelson to resort to riding a bicycle.
After killing a flying bat-like creature which carries the mind control device, Dr. Nelson returns home to find his wife newly assimilated. She then attempts to force his own assimilation using another bat-creature in her possession, and he ends up being forced to kill her in self-defense. By then, the only people who are still free from Zontar's influence are Nelson, Anderson, Anderson's wife, and a group of army soldiers on station in the nearby woods.
Nelson finally persuades the paranoid Anderson that he has made a horrible mistake in blindly trusting Zontar's motives, allying himself with a creature bent on world domination. When they discover Tom's wife has taken a rifle to the alien's cave in order to kill it, they hurriedly follow her; but the creature kills Claire Anderson before the two doctors can rescue her. Finally, seeing the loss of everything he holds dear, Dr. Anderson viciously attacks Zontar by holding a blowtorch to the creature's face; Anderson dies at the alien's hand as it expires.
It Conquered the World was written by Lou Rusoff, but before being completed, Rusoff's brother died and he had to leave for Canada. Roger Corman then called in Charles Griffith to do a final rewrite, two days before filming began; Griffith, however, didn't want his name to be credited on screen.
The design of the creature was Corman's idea, and he thought that coming from a big planet, It would have evolved to deal with heavy gravity and would therefore be low to the ground. Corman later admitted this was a mistake, saying the creature would have been more frightening had It been larger or taller. When Beverly Garland first saw the creature, she commented "That conquered the world?" and kicked It over. Griffith:
I called it Denny Dimwit and somebody else called it an ice-cream cone. I was around when Paul Blaisdell was building it, and he thought the camera would make it look bigger. I have some photographs of it in construction, probably the only ones in existence. I asked for my name not to be on that picture, so I was unbilled. Surprisingly, it got good reviews.
It Conquered the World was released theatrically by American International Pictures in July 1956 on a double bill with The She Creature.  During the 1960s, the film was syndicated to television by American International Television. VHS versions appeared in the 1990s on the US home video market (RCA Columbia Home Video) but these are no longer in distribution, nor is the film available on DVD or Blu-ray in the US or in the UK.
Before its theatrical release in England, British censors expressed concern about the scene near the end where the creature is destroyed by a blowtorch, on the grounds that it depicted cruelty to animals. AIP successfully argued an enemy alien from outer space was not an animal.
Film historian and critic Leonard Maltin called It Conquered the World, "... well acted and interesting but awkwardly plotted." Time Out magazine, however, gave the film a negative review, criticizing the film for its poor special effects. He opined, "You have to see a movie like this to realise that film-makers who feel they have nothing to lose are rarer than you'd think."Chicago Reader gave the film a generally positive review, saying "Amazingly, this 1953 picture isn't half bad […]."
All Movie Guide gave the film three out of five stars, calling it an "above-average quickie."
In popular culture
In 1966, It Conquered the World was remade in 16mm color by self-proclaimed "schlockmeister" Larry Buchanan after he secured rights from AIP; he retitled his rewritten remake Zontar, the Thing from Venus and then sold it to television syndication.
Frank Zappa's 1974 live album Roxy & Elsewhere referred to the film in the introduction for the song "Cheepnis".
The end of the film was shown at the beginning of Elvira, Mistress of the Dark (1988).
In 1991, It was the subject of the comedy television series Mystery Science Theater 3000; joke topics included poor monster props, occasionally wooden acting and an overblown closing monologue.
Audio samples from the film were included in the song "Facing That" from M83's self titled debut album, released in 2001.