John Smith (Tenth Doctor)

John Smith was a Human from Earth, although he was formed from the Doctor when he used a Chameleon Arch to turn himself into a Human to escape the Family of Blood. The name "John Smith" was actually one of the Doctor's many aliases.

His cover story was that he was a teacher and Martha Jones was his family's maid, although since his parents, Sydney (a watchmaker from Nottingham) and Verity (a nurse), had died, she only had him to serve.

Despite his humanity, he showed some incredible skills, most likely from the Doctor, such as the ability to throw a cricket ball to an exact point, starting a chain reaction and saving someone and her baby from being crushed by a falling piano by causing a barrel to roll in the way of the pram, halting it. (DW: Human Nature)

On the other hand, he was also far more emotional than the Doctor, who could often appear heartless, and burst into tears when he learnt that he had to sacrifice himself and become the Doctor again, and so would have to leave his love, Joan Redfern, and "die". However, he had to save her and the rest of Humanity, so he did finally sacrifice himself and become the Doctor again, although the Doctor assured Joan that John Smith was still somewhere in his mind.

At one point Smith/Doctor envisions a possible future in which he and Joan marry, have children, grow elderly, and Smith ultimately passes away from old age.

Behind the Scenes

 * His parents Sydney and Verity were references to Sydney Newman and Verity Lambert, the Creators of the early Doctor Who.
 * In his video diary (released with the Series 3 DVD set), David Tennant remarks that the makeup used to make him look elderly (in the "alternate future" sequence) made him look uncannily like his real-life father.