The Chameleon Arch is a device that rewrites every cell of an individual to a specific species. The conversion, which causes extreme pain, also provides a set of false memories to match the new persona. The Tenth Doctor uses it in “Human Nature”, enabling him to hide from the Family of Blood in 1913 as the school teacher, John Smith. He retains a small amount of “residual awareness”, resulting in dreams about his life before the change. The Chameleon Arch stores the Doctor’s Time Lord identity in a fob watch that slots into the device as it is operated. In “Utopia”, Martha discovers that The Master used the same process, generating “Professor Yana” as his persona.
He never raised his voice. That was the worst thing. The fury of the Time Lord. And then we discovered why. Why this Doctor, who had fought with gods and demons, why he’d run away from us and hidden—he was being kind.
He wrapped my father in unbreakable chains, forged in the heart of a dwarf star. He tricked my mother into the event horizon of a collapsing galaxy to be imprisoned there…forever. He still visits my little sister once a year every year. I wonder if one day he might forgive her, but there she is—can you see? He trapped her inside a mirror, every mirror. If ever you look at your reflection and see something move behind you, just for a second, that’s her. That’s always her. As for me, I was suspended in time. And the Doctor put me to work……standing over the fields of England…as their protector.
We wanted to live forever, so the Doctor made sure that we did.