"Ka Faraq Gatri" was an epithet applied to the Doctor by the Daleks, which translated as "Destroyer of Worlds"; (PROSE: Timewyrm: Revelation) or possibly, "Nice guy, if you're a biped". (PROSE: Continuity Errors)
The Doctor was aware of this as early as their second incarnation. After an encounter with a group of Daleks who had referred to him as "the Ka Faraq Gatri", Victoria Waterfield asked the Doctor what it meant. He dismissed it as "silly superstition". (COMIC: Bringer of Darkness)
According to another account, Ruath understood that the Doctor, whilst in his fifth incarnation, had yet to become the Ka Faraq Gatri. (PROSE: Goth Opera)
The Renegade Daleks identified the Doctor, by this point in his seventh incarnation, on sight as the Doctor, their greatest foe, and the "Ka Faraq Gatri". (PROSE: Remembrance of the Daleks) The Daleks once again awarded the name to the Doctor upon orchestrating the destruction of the Dalek home planet Skaro. (PROSE: Timewyrm: Revelation)
It was used once again by Karpagnon in reference to a fictional Doctor. (PROSE: The Terror of the Umpty Ums)