When the Family of Blood, armed with a stolen vortex manipulator, came after the Tenth Doctor, he decided that it would be best if he and his companion, Martha Jones, hid for a few months waiting for the Family to exhaust their limited lifespan. Since the Family of Blood could track by scent but never saw his face, he used the Chameleon Arch to change his biology and transform into a human, storing his Time Lord essence in a special fob watch. The TARDIS invented a life story for him, chose a setting and integrated him. This led to the Doctor living life as an ordinary schoolteacher named John Smith in 1913, believing himself to be human and believing his TARDIS created memories to be real.