Light ( Ghost Light ) Light was a traveller who journeyed through the universe making a Catalogue of Life , described by the Seventh Doctor as an " evil older than Time itself . " Characterisitics . Light ' s form depended upon his environment . When he awoke he " naturalised " in an angelic human form , majestic and imposing , glowing with a yellow light and wearing a yellow robe . In 1883 , the Seventh Doctor told Ace that he moved at the speed of thought , teleport ing in a flash of lightning and thunder . Additionally , he possessed telekinesis and could telepathically kill someone , causing them to glow blue with electricity . He could also highlight microscopic organisms and dismember , petrify , and convert humans into primordial soup . His angelic appearance wildly contrasted with his bewildered , frustrated behaviour , doddering speech pattern and screeching timbre . Depending on his mood , he could speak in a timid warble or an angered snarl . Light had an all - consuming detestation of change , even finding the idea of himself changing to be nonsense . ( TV : " Ghost Light " ) Biography . Light was an Eternal ( PROSE : " Divided Loyalties " ) who travelled the universe , taking it upon himself to catalogue all organic life . Assisting him in his Catalogue of Life was the Survey kept under Control , and all three travelled in Light ' s ship . On prehistoric Earth , he faithfully catalogued all life , including taking the Neanderthal Nimrod as a specimen , having been worshipped by Neanderthals as " the Burning One . " But no sooner had he finished cataloguing life on Earth than it all started changing . For unknown reasons Light went into hibernation and the ship remained in what would become Africa . Meanwhile , the Survey got out of control and began adopting different forms of dominant life , but remained fearful of Light ' s return . While hunting in Africa , Redvers Fenn - Cooper claimed to have seen a dazzling light , noting that it had wings and other features . Afterwards , the ship was moved below Gabriel Chase in Perivale . Survey became " Josiah Samuel Smith " and ran the house , keeping Control locked in the ship . After the Seventh Doctor and Ace arrived , Ace accidentally awoke Light and the Doctor " promised " Control her " freeness " . Asleep for millennia , Light didn ' t believe he was on Earth because it was different . To determine this , he killed a maid and took apart to see how she worked . He became angry that even microbes were evolving ; everything on Earth had changed and his Catalogue was ruined . He then killed Inspector Mackenzie , turning him into primordial soup , which he planned to do to Earth . After turning Lady Pritchard and her daughter Gwendoline to stone , he decided Earth ' s fate . Since the primordial soup would start to evolve again , he would stop the change , eradicating all organic life in the " firestorm program . " The Seventh Doctor showed Light that he himself was evolving , since he was no longer his original shape . He asked Light why his Catalogue didn ' t include gryphons , basilisk s , dragon s , bandersnatch es , slithy tove s , the crowned Saxe - Coburg and other creatures Light didn ' t know . Confused as to why these weren ' t in his Catalogue , Light refused to accept that even he had evolved . To prevent himself from changing , Light dispersed himself . ( TV : " Ghost Light " ) Behind the scenes . The Doctor ' s comment that Light travels at the speed of thought is a play on the fact that thought supposedly travels at the speed of light .