The Doctor ( Battlefield ) An incarnation of the Doctor was one of many to have accounts claim that he would one day become Merlin . This version was seen when one of his previous incarnations looked into a Tomorrow Window . Biography . The Doctor and his companion Anna travelled to Exeter in the 21st century where they encountered one of the Doctor ' s previous companions , Tegan , who cursed the Doctor for what her time with him had done to her . Later in the TARDIS , Anna found a diary that Tegan had kept during her travels in the TARDIS . The diary warned the reader that the Doctor manipulated his companions into killing for him . Anna realised that this had happened to her and asked the Doctor to take her home , which he reluctantly did . ( PROSE : " Good Companions " ) After finding another companion , Guinevere Winchester , the Doctor was sent by the Time Lord s to the Schrödinger Institute , a research station in deep space where sabotage had caused a temporal echo to occur . The temporal echo meant that the Doctor and Guinevere could not be seen by anyone or even touch anything until someone else did so . The Doctor managed to rewire a control box after a technician had worked on it . This broke the echo , allowing the Doctor and Guinevere to leave . ( PROSE : " Revenants " ) Travelling alone , the Doctor went to visit his old friend , Greenaway . The Doctor told Greenaway that his life support machine was unable to keep him alive any longer . In an act of mercy the Doctor turned off the machine and left in his TARDIS , unaware that Greenaway managed to survive . ( PROSE : " Greenaway " ) The Doctor once visited the Braxiatel Collection and found a diary in the archive that Jason Kane had kept whilst he was stranded in the past . The Doctor travelled back in time and brought Jason back to the future . The Doctor then kept Benny and Jason ' s wedding rings as a memento . ( PROSE : " The Collection " ) According to some sources , the Doctor became known as Merlin , and resided in Arthur ' s World for some time . Merlin fought Morgaine in this reality on several occasions . After she bound him in ice in Breceliande , the Doctor summoned a dragon to melt it . Songs were sung among the people of the Doctor ' s " power over light , darkness and the elementals " . He taught King Arthur since he was a child , and saved his life on many occasions . When Arthur was old and had almost lost the battle to Morgaine , Merlin spoke with him of how the battle would end . Merlin took Excalibur from him and sent it back in time so that his previous incarnation would use it to defeat Morgaine . ( PROSE : " Battlefield " ) Merlin later sent Excalibur to Winifred Bambera and Ancelyn so that they could prevent the Deindum from causing Phobos and Deimos to break away from their orbit of Mars . Because he needed to be " somewhere else " , he used a hologram to speak to Bambera and Bernice Summerfield when they reached the chamber in which Excalibur could be used . ( PROSE : " Excalibur of Mars " ) Appearance . This Doctor wore a mustard yellow waistcoat over a crumpled white dress shirt , open toed sandals and socks , bracelets , and a tatty Afghan coat . He had curly red hair and was very short . ( PROSE : " Battlefield " , " Revenants " ) He also had a strong scent of cologne . ( PROSE : " Greenaway ) " Behind the scenes . Peter Anghelides has said this incarnation is partly based on one of his university friends and that he is meant to be the Merlin Doctor from Marc Platt ' s novelisation of " Battlefield " . However , the incarnation of the Doctor seen in the novelisation is not the only one to have supposedly become Merlin . Muldwych long has been speculated by fans to be Merlin , and the Eighth Doctor took over the role in " One Fateful Knight " . The Tenth Doctor later claimed that he was once called Merlin by King Arthur . ( COMIC : " Fugitive " ) A ginger haired future incarnation of the Doctor was set to appear in " Doctor Who : The Last Regeneration " by Lee Sullivan , but the comic was cancelled .