Forbidden PlanetForbidden Planet is a classic 1956 science fiction film. The film features a number of spectacular special effects and was the first screen appearance of the famous Robby the Robot; the film's plot is generally described as (extremely loosely) based upon Shakespeare's The Tempest.
Warning: Wikipedia contains spoilers
In the film, a starship from Earth arrives at a planet of Altair to find out what happened to an expedition to that star some twenty years previously; on arrival, they find the ship being scanned by some immense power source, and they are contacted by the sole survivor of the expedition, Doctor Morbius (Walter Pidgeon). On landing, they are met by Robby the Robot, who takes them to Morbius' house. Morbius explains that within a year of the expedition arriving, some unknown force had wiped them out overnight, except for himself and his infant daughter. He fears the same may happen to the starship, though he has no fears for himself, as he and his daughter have been unharmed since then, and his house has an interesting array of high-tech defences. The captain Leslie Nielsen queries such technological abilities on the part of Morbius, whose speciality, as a philologist on the original expedition, had been in languages.
Morbius shows the captain what he has been working on for the last twenty years. He had been reconstructing the history, and some of the minor technologies (such as Robby) of the Krell, the planet's native race, who had all died in one mysterious night of total destruction, a quarter of a million years before. He shows tham a Krell nursery; this includes an "education machine" that instantly killed one person who tried it, and put Morbius himself into a coma for weeks, though he recovered with an enormously increased intelligence. Then he shows them the interior of the planet, where a vast underground machine, powered by tens of thousands of fusion reactors, has been operating, self-repairing and self-maintaining, for some unknown purpose, for all the millennia since the death of the Krell. The effects shots of the Great Machine are well done, showing miles-deep shafts, with huge and incomprehensible structures moving up and down, and vast energy discharges passing between them. (The 1990s television series Babylon 5 also had a Great Machine beneath a planetary surface, and some of the visual effects of that are plainly done as a homage to the machine in Forbidden Planet.)
Things get interesting for the captain when he meets Morbius' beautiful but extremely naive daughter Altaira (Anne Francis); now nineteen years old, she is very curious about human relations, and the captain, establishing the tradition so avidly followed by James T. Kirk, enlightens her on some aspects of this. At night, while Morbius sleeps in the Krell nursery, and power meters all round the walls start going off the scale, the ship comes under attack from some invisible being made of pure energy. Morbius is awakened by his daughter screaming from a nightmare; the attacker vanishes and the power meters revert back to zero as he wakes up... The starship's doctor sneaks in to use the education machine; though he dies from its effects, he gasps out his realisation of what killed the Krell; the huge machine was for the materialisation of any object desired, making the Krell able to produce anything they wanted at a mere thought. But: "They forgot one thing, John. Monsters! Monsters from the Id!"
Though the Krell considered themselves civilised, their unconscious minds also had access to the machineries, and the race was wiped out in one night of frenzied destruction as the Great Machine enabled the acting out of their unconscious urges. In the confrontation that follows with Morbius, he realises that his session with the Educator had attuned his mind to the machinery, and he (or, rather, his wish to be left alone to study the Krell) had been responsible for the deaths of the rest of the expedition. Though he realises that his daughter is of an age where she really should be meeting other people and forming relationships, other, darker desires of his have control over the machinery, prompting the attack on the starship that might take his daughter away. The film ends with Morbius' suicide, as the only means to protect everyone else from destruction by another Machine-powered monster, and the triggering of the self-destruction of the Machine as too dangerous to be used by any race without full control over its mental processes.
Overall, though it preceded the television series by some years, Forbidden Planet is remarkably like one of the better Star Trek episodes: it could easily have been (but never was) adapted as an episode in that series, complete with the starship captain's amorous entanglements with the girl. Gene Roddenberry admitted in his biography "Star Trek Creator" that Forbidden Planet was one of the inspirations for Star Trek.
Robby the Robot was possibly the most expensive film prop ever constructed at the time: he also featured in the film The Invisible Boy. He made a cameo appearance in the 1980s film Gremlins; he can be seen in the background during a telephone conversation scene at an inventor's convention.
Forbidden Planet is also the name of a science fiction and fantasy bookshop in London, England, that began life as a small store and susequently expanded into much larger premises on New Oxford Street, then added a chain of smaller shops across the UK and Ireland. On September 30, 2003 the London branch moved to even bigger premises at the eastern end of Shaftesbury Avenue.