Diamond Jack

 was a showman and a magician. Captain Mike Yates said that people who watched his show died from being frozen. He made Jo Grant disappear and knew of the Third Doctor and his TARDIS. He later placed Jo in his house. He had no memory of his own, so had to steal others, such has how Jo became a member of UNIT. He was connected to a machine that was found underneath a cemetery, it saved the memory of an alien, his true self. He was exiled to Earth and had his memories wiped but still had his powers. (AUDIO: The Magician's Oath)