Star Wars?

A couple paragraphs from Wookiepedia. The evolution of the series was a complicated one.

Lucas' original concept was a swashbuckling space adventure movie. He says "the film was a good concept in search of a story." He first tried to have a child buy the rights to remake Flash Gordon, but was unsuccessful.
In 1971, United Artists agreed to make American Graffiti and Star Wars in a two-picture contract, though they would reject Star Wars in its early concept stages. Graffiti was made first and when it was completed in 1973, Lucas set to work on making his space adventure movie. In early 1973, Lucas wrote a short summary called "The Journal of the Whills", which told the tale of the training of apprentice C.J. Thorpe as a "Jedi-Bendu" space commando by the legendary Mace Windy.
Frustrated that his story was too hard to understand, Lucas then wrote a 13-page treatment called The Star Wars, which was a loose remake of Akira Kurosawa's The Hidden Fortress. By 1974, he had expanded the treatment into a rough draft screenplay, which added elements such as the Sith, the Death Star, and once more had the protagonist as a young boy, named Anakin Starkiller. For the second draft, Lucas made heavy simplifications, and also introduced the young hero on a farm, with his name now Luke rather than Anakin. Luke/Anakin's father is still an active character in the story at this point, a wise Jedi knight, and "the Force" now became a supernatural power. The next draft removed the father character and replaced him with a substitute named Ben Kenobi, and in 1976 a fourth draft had been prepared for principal photography. The film was titled "Adventures of Luke Starkiller, as taken from the Journal of the Whills, Saga I: The Star Wars." During production, Lucas changed Luke's name to Skywalker and altered the title to just "The Star Wars" and finally "Star Wars".
At this point, Lucas was thinking of the film as the only entry that would be made — the fourth draft underwent subtle changes that made it more satisfying as a self-contained film that ended with the destruction of the Empire itself, as the Death Star was said to achieve; possibly this was a result of the frustrating difficulties Lucas had encountered in pre-production during that period. However, in previous times Lucas had conceived of the film as the first in a series of adventures. The second draft contained a teaser for a never-made sequel about "The Princess of Ondos", and by the time of the third draft some months later Lucas had negotiated a contract that gave him rights to make two sequels. Not long after, Lucas met with author Alan Dean Foster, and hired him to write these two sequels — as novels. The intention was that if Star Wars was successful — and if Lucas felt like it — the novels could be adapted into screenplays. He had also by this point developed a fairly elaborate backstory — though this was not designed or intended for filming; it was merely backstory. "The backstory wasn't meant to be a movie," Lucas has said.