The movie's opening prologue in the English version states: "Metropolis, known ages ago as planet Earth, now faces its gravest hour. Lord Graal, has just escaped from the prison - satellite where his brother - ruler of the peaceful, galactic democracy had exiled him. Malevolent and power-hungry, Graal has plans of vengeance that might forever alter the destiny of mankind".
This Italian motion picture is considered a gratuitous clone, rip-off or knock-off of Star Wars: Episode IV - A New Hope (1977). The picture was widely distributed globally by the Columbia Pictures studio.
The name of the planet was Metropolis. The name had itself been the title of a famous b&w silent science-fiction film directed by Fritz Lang [See: Metropolis (1927)]. Around five years after The Humanoid (1979), that film would get a major re-issue with a new score composed by Giorgio Moroder. The Metropolis planet in The Humanoid (1979) replaced a former name of the planet, that being Earth. Ironically, in the film's closing epilogue, the planet is referred to as Earth and not as Metropolis.
The trivia item below may give away important plot points.
The film's closing epilogue in the English print states: "Once again Planet Earth had narrowly escaped disaster. Once again, it had found in itself the intelligence, the insight and the strength to repel a mortal enemy. Once again, man was to live at peace in the galaxy".