After the Second Doctor was exiled to earth for homosexuality and forced to regenerate, Pertwurst took over working alongside the Brigadier and UNIT.
The Third Doctor is the name used to refer to the third incarnation of the Time Lord known as the Doctor. The Third Doctor was played by Jon Pertwee.
The technological limits of the time period, and the constraints of his exile, often made him frustrated and bitter. However, he retained his endearing compassion toward his human companions, and he finally began to gain some mastery over his TARDIS as he dissected its inner-workings while it was rendered inoperable. This incarnation of the Doctor worked for UNIT as their unpaid scientific advisor, and remained in their service after his exile was ended. Unlike his earlier incarnations, he was quite willing to engage others physically, and cut a more dashing figure.