Doctor Who is a British science-fiction series written for television and produced by the BBC since 1963. The show revolves around an extraterrestial creature from the planet Gallifrey called a Time Lord who carries the name The Doctor and who explores the universe in his space ship and time travelling machine TARDIS. Doctor Who has gained a considerable following over the decades and the show has grown into something of a cult series for many generations. The show's main character, Doctor Who, has been played as of 2017 by twelve different actors, which has been explained with the help of the concept of regeneration into a new incarnation. This format was brought into life as way to continue the show after the original lead William Hartnell had fallen very ill in 1966.