Doctor Who is a British science fiction television programme produced by the BBC. The programme depicts the adventures of a mysterious alien time-traveller (called a Time Lord) known as "the Doctor" who travels in his time and spaceship, the TARDIS, which normally appears from the exterior to be a blue 1950s police box. With his companions, he explores time and space whilst facing a variety of foes and righting wrongs. The programme is listed in Guinness World Records as the longest-running science fiction television show in the world, and as the "most successful" science fiction series of all time, in terms of its overall broadcast ratings, DVD sales, book sales and iTunes traffic, as well as "illegal downloads." It has been recognised for its imaginative stories, creative low-budget special effects during its original run, and pioneering use of electronic music. The show is a significant part of British popular culture; in the United Kingdom and elsewhere, it has become a cult television favourite and has influenced generations of British television professionals, many of whom grew up watching the series.