Kahler - Tek Kahler - Tek , later known as the Gunslinger , was an experimental Kahler cyborg created by Kahler - Jex . Biography . Kahler - Tek was originally from Gabrean on Kahler . He was one of many who were experimented on by Kahler - Jex and his team to create a soldier s that would end the war their people were engaged in . Tek was transformed into a cybernetic war machine along with countless others who ended the war within a week . ( WC : " The Making of the Gunslinger " ) However , during that time Kahler - Tek was damaged in the field leading to the resurgence of his original personality . This meant he did not obey his pre - programmed instructions to deactivate after the war ended and began hunting down the scientists who experimented on him . After many years he tracked the remaining two scientists to Earth . He found the first in the American desert who tried to appeal to his original nature but the cyborg executed him anyway . He tracked his final target , Kahler - Jex , to the town of Mercy where he had become the town doctor . He then placed the town under siege , as if he went in , innocent people may have gotten in the way of his gunfire , so he waited , suspecting they would throw him out . However they didn ' t . Three weeks later , the Eleventh Doctor arrived with his in - laws , Amy and Rory and learned about the Gunslinger ' s presence in the area . After learning what Kahler - Jex had done to him , the furious Doctor threw him out of the town but allowed him to return before the Gunslinger could kill him . Tek accidentally killed Jex ' s friend , Isaac , who sacrificed himself to save Jex from the Gunslinger ' s energy beam . Frustrated , Tek warned that he would return the next day and kill everyone unless the Doctor handed Jex over . Tek returned , as he had promised but did not go on a murderous rampage , sparing everyone in the town despite the threat he ' d made the day before . When he realised that Jex had left he was enraged but Jex contacted him from his ship , expressing regret about what he had done to him . Tek demanded that Jex return and face him but instead Jex chose to commit suicide . Believing that he no longer had a purpose , the Gunslinger decided to go into the desert and self - destruct but the Doctor persuaded him to stay and act as the town ' s protector . ( TV : " A Town Called Mercy " ) Personality . Kahler - Tek was strongly motivated by vengeance . He was determined to kill the entire team of scientists that had turned him into a cyborg . However , he demonstrated an unwillingness to harm innocent people . Although he threatened to kill everyone in the town of Mercy , he did not intentionally harm any of the people that lived there , even though they had not handed Kahler - Jex over to him . After Jex committed suicide , the Gunslinger felt that he no longer had any reason to live and decided to go into the desert and self - destruct . The Doctor convinced him to stay and act as a protector to the town . ( TV : " A Town Called Mercy " ) Abilities . Built to be a weapon , Kahler - Tek was armed with a powerful energy weapon . The weapon was linked to an automatic targeting computer , capable of calculating the probability of harming innocents , advising him based on this to either disengage or terminate the target . He also had sensors that could see through walls and rocks , and identification software that could seemingly detect heartbeats and vital signs and identify Kahler markings . He also possessed a short - range teleport . ( TV : " A Town Called Mercy " ) Other Information . When cyborg hacker Psi was attempting to protect Clara Oswald from the Teller , he ensured that it would focus on his guilt by uploading the memories of some of the worst criminals in history , one of them being Kahler - Tek . ( TV : " Time Heist " )