Known only to science fiction fans as the Doctor, a being who explores the timeline in order to save the world from dangers both mysterious and impossible, the BBC's Dr. Who is the longest running sci-fi TV series of all time, and the secret to its longevity is the ability to recast the lead actor as the same character. The Cast of Dr. Who takes you back in time to explore the personal histories of ten men who have portrayed the BBC's enigmatic, often eccentric, time travelling hero.