K was a man who attempted to steal the energy from the Tenth Doctor's TARDIS.
K once had a brother who was killed by a speeding trade ship.
He created the illusion of a space station on the surface of a planet and grounded the TARDIS there. He showed the Tenth Doctor footage, most of which was faked, and attempted to confiscate his TARDIS as punishment. However, the Doctor knew his plan all along, and broke the illusion before leaving K on his planet. (COMIC: Ground Control)