John Williams is one of the most important film composers of the past 50 years, and the most important composer of science fiction/fantasy film music of all time. He has been nominated for a whopping 49 Academy Awards, and won five of them -- for Fiddler on the Roof, Jaws, Star Wars, E.T., and Schindler's List. He has been nominated for six Emmy Awards, and won three of them -- for Heidi, Jane Eyre, and Great Performances (theme). He holds the record for the most Oscar nominations for a living person, and is the second most nominated person in Academy Awards history (behind Walt Disney's 59).
Among his most sci fi/fantasy scores are The Poseidon Adventure, The Towering Inferno, Jaws, Star Wars, Close Encounters of the Third Kind, Superman, The Empire Strikes Back, Raiders of the Lost Ark, E.T, Return of the Jedi, Indiana Jones and the Temple of Doom, The Witches of Eastwick, Indiana Jones and the Last Crusade, A.I. Artificial Intelligence, Harry Potter and the Sorcerer's Stone, and Harry Potter and the Prisoner of Azkaban.
Although nominated three times for an Oscar, it was 1974's Fiddler on the Roof that made him famous. Yet, today, it is his soundtracks for Jaws, Star Wars, Close Encounters of the Third Kind (written the same year as Star Wars), The Empire Strikes Back, and Raiders of the Lost Ark which the public remembers.
Steven Spielberg, with whom Williams had worked on Jaws, recommended Williams to George Lucas when Lucas was looking for a composer to score his Star Wars.
Lucas asked for an old-fashioned soundtrack, and played several movie soundtracks over rough footage to give Williams an idea of what sort of music he wanted for each segment of the film. (This is a common technique with directors.) Initially, Lucas pressed for an ADAPTED SCORE -- one using existing music, but adapted minimally for the film. Three of Williams' first four Oscar noms were for adapated scores...
Williams convinced Lucas that an original music would be better.
Williams uses a style of music called Romanticism, which focuses on strong emotion -- particularly intuition and awe. Romanticism flourished in the 1800s, and included composers like Beethoven, Franz Liszt, Frédéric Chopin, Giuseppe Verdi, Hector Berlioz, and Felix Mendelssohn. Williams has an extreme fondness for warm brass. Based on the musical ideas Lucas had in mind, Williams decided to write Star Wars with something called leitmotifs -- a different "theme" for each character or incident. Thus you have Luke's Theme, Leia's Theme, Vader's Theme (the Imperial March), etc.
Williams cites Erich Wolfgang Korngold's theme for the 1942 film King's Row as a heavy influence for the "Star Wars: Main Title Theme". (Korngold was the greatest film composer in the world from 1930 to 1960, and his Robin Hood is considered the greatest soundtrack ever. Korngold was the first to use the leitmotif in a film soundtrack.) Williams also cited Alessandro Cicognini's soundtrack for 1948's Italian Neorealism film The Bicycle Thief for the segment "Dune Sea of Tatooine/Jawa Sandcrawler". Williams took six weeks to write the score (which is typical for most Hollywood films), working with an orchestrator and plucking out themes on a synthesizer.
In March 1977, Williams recorded the soundtrack in a swift 12 days with the London Symphony Orchestra. Film composer Andre Previn was the one who hooked Williams up with the LSO. The soundtrack was recorded in Dolby stereo, which was highly unusual for the time. (Most films did not have a stereo soundtrack until after Star Wars.)