The savage irony for the Tenth Doctor is that Wilfred Mott (played by Bernard Cribbins), grandfather of Donna Noble and starstruck fan of the Doctor and all of his works, is not only the exception to the rule, but the fate-sealing proof of it too.
We first encounter Wilfred as a newspaper seller in an abandoned London in Voyage of the Damned. His role was intended originally to be just a one-off, but when the actor playing Donna’s father became ill, steps were taken to re-introduce Wilf as her grandfather. Necessity being the mother of invention, this excitable, star-gazing allotment-dweller soon became a firm favorite.
Go check out Anglophenia’s great writeup of Wilf