to invest in. By 1974, he had expanded the story into the first draft of a screenplay. Fox expected the film would be of limited financial success, and so it was given a relatively low budget, with production being moved to Elstree Studios in England to help save on cost. Many of the scenes were shot in England, and so featured a number of British actors. The Star Wars robots were built by the small English company Peteric Engineering. A 2019 BBC documentary revealed how the parts required to create these machines and other now iconic film props, including the light sabers (originally called 'laser guns'), were ingeniously recycled from items scavenged in junk shops, ever conscious of the need to spend as little money as possible. The 1977 movie's success led Lucas to make it the basis of an elaborate film serial. With the backstory he created for the sequel, Lucas decided that the series would be a trilogy of trilogies. Most of the main cast would return for the two additional installments of the original trilogy, which were self-financed by Lucasfilm. Star Wars was released on May 25, 1977, and first subtitled Episode IV: A New Hope in the 1979 book The Art of Star Wars. Episode V: The Empire Strikes Back was released on May 21, 1980, also achieving wide financial and critical success. The final film in the trilogy, Episode VI: Return of the Jedi was released on May 25, 1983. The story of the original trilogy focuses on Luke Skywalker's quest to become a Jedi, his struggle with the evil Imperial agent Darth Vader, and the struggle of the Rebel Alliance to free the galaxy from the clutches of the Galactic Empire. Prequel trilogy According to producer Gary Kurtz, loose plans for a prequel trilogy were developed during the outlining of the original two films. In 1980, Lucas confirmed that he had the nine-film series plotted, but due to the stress of producing the original trilogy, he had decided to cancel further sequels by 1981. In 1983, Lucas explained that "There was never a script completed that had the entire story as it exists now ... As the stories unfolded, I would take certain ideas and save them ... I kept taking out all the good parts, and I just kept telling myself I would make other movies someday." Technical advances in the late 1980s