The Gunslinger, formerly known as Kahler-Tek, is the main villain in the Doctor Who episode A Town Called Mercy, He was an experimental Kahler cyborg created by Kahler-Jex.
He is portrayed by Andrew Brooke.
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.
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 soldiers 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. 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.