Xoanon Xoanon was a supercomputer meant to guide the Mordee expedition . He eventually developed into a new , living creature and subsequently became " the most powerful computer ever built " . He inadvertently became insane when the Fourth Doctor helped repair him , and became a god to the human s whose development he guided . Form . Xoanon existed within the main computer complex , later called the " Sacred Heart " by the Tesh , a room composed of several screens with a sphere - like podium in the middle which held a hexagonal screen that flashed as he spoke . The only face he ever projected was that of the Doctor ' s and these appeared on screens and as three - dimensional " phantoms " . ( TV : " The Face of Evil " ) Abilities . Xoanon was linked throughout the Mordee ship , able to watch and control various parts of it through sensory links everywhere . This allowed him to measure temperature , vibrations , pressure , and let him know where anyone was on the ship . He could even electrify the walls or throw the atomic generators into overload to blow up half a planet . He could project a beam of white light to harm individuals and could psychically control people , though this control could be interrupted if he became distracted . He could also completely dematerialise people or materialise objects from nothing . Xoanon was separated from the Sevateem village by the Black Wall , a time barrier that pushed the inside of the Wall forward in time a few seconds , preventing any energy or anything physical from passing through . Xoanon could communicate to Neeva through Mordee technology along a tight - beam transmission , allowing his voice to penetrate the barrier . The phantoms that attacked the Sevateem were psi - tri projections of Xoanon ' s face , which hunted by movement or sound and could crush their targets easily . They were separated from the Sevateem ' s village from the Boundry , an invisible wall created by low - intensity sonic discruptors which Xoanon could shut off . ( TV : " The Face of Evil " ) Biography . Birth . When the human Mordee expedition arrived on a jungle world , the computer broke down and repairs were made by teams for generations . Unbeknownst to them , the work had resulted in Xoanon evolving into a living creature . Just after his " birth " when he was still in shock , the Doctor arrived and assisted in the repairs . He failed to recognise the birth trauma , assuming the data - core to be damaged , and renewed him by making a direct link with the Doctor ' s brain . Instead of taking only compatible information like a computer should , Xoanon also took the Doctor ' s personality . He awoke with one personality , only to have his own manifest . He went mad , becoming omniscient and schizophrenic after the Doctor had left . ( TV : " The Face of Evil " ) Insanity . Making his madness a reality , Xoanon created two tribes from the humans : the Sevateem ( a corruption of " Survey Team " ) which were primitives that represented independence , strength , boldness , and courage ; and the Tesh ( " Technicians " ) who were more technological and represented self - denial , control , and telepathy . The phantoms were even representations of the darker side of Xoanon ' s id . He created a world in his own image , making the tribes hate each other to act out his torment . He told himself he was breeding a race of super - humans , using hostility and conflict to speed up the process until he was ready to select the best from both groups . ( TV : " The Face of Evil " ) Legends . The myths of the humans told of Xoanon and the Evil One , both of which shared the same voice as it was the Doctor ' s . The Sevateem worshiped Xoanon as a distant god who communicated only with the high priest Neeva . He was held captive by the Evil One and the Tesh within the Black Wall wherein lay Paradise . Their sign of warding off evil was also the method for checking the seals of a Starfall Seven spacesuit , and they believed the Tesh to have silvery skin and two heads , one within the other . This came about from the Tesh wearing spacesuits . The Tesh believed the " Lord of Time " would return one day to help them and worshiped Xoanon who existed within the Sacred Heart ( main computer complex ) . They viewed their intelligence and superior yet nothing compared to the savage Sevateem . " The flesh is strong and we are weak " was a saying of theirs . ( TV : " The Face of Evil " ) Return to sanity . Upon the Doctor ' s return to the Mordee expidition , Xoanon was compelled to free himself of " us " ( being both Xoanon and the Doctor ) . Recognising his mistake , the Doctor intended to remove his half of Xoanon ' s dual personality . He even met Xoanon and told the computer his own history , the multiple personalities enjoying the story until the Doctor revealed that the " poor machine - man " Xoanon felt sorry for was indeed Xoanon . He questioned the Doctor , the voices repeatedly asking , " Who am I ? " as they believed they were Xoanon and could not acknowledge that the Doctor was separate and real . Xoanon was taken over by a longing to " destroy and be free " . As the Sevateem and Tesh readied to destroy themselves , the Doctor searched for a way to wipe his personality , as Xoanon prepared to detonate the atomic generators of the Mordee ship . He would rather destroy himself and everything before allowing himself to be wiped . Xoanon took control of the tribes to kill the Doctor , but was confronted by Neeva whom he obliterated . This distracted the tribes and the Doctor connected his brain with Xoanon once more . The Doctor ' s personality was erased and Xoanon was whole again . He felt extremely sorry about what he had done , but now that it was over , was willing to help the tribes . He offered his great power and knowledge to them and even offered his self - destruct button as a token of good faith . Pressing it would make Xoanon cease to exist , yet neither tribe could do it . The Doctor then left Xoanon , the Sevateem , and the Tesh to their own devices . ( TV : " The Face of Evil " )