Doctor Who

Doctor Who stands as the genre's endurance champion: the longest-running science fiction show in the world has regenerated across six decades and fifteen Doctors. The TARDIS sound is recognized by virtually every person in the country, a cultural saturation unmatched by any other series on this list. Concrete evidence of its impact: since 2005, the rebooted series has maintained an average audience of 8.2 million viewers per episode in the UK alone. Compared to Downton Abbey (#8), which mastered period drama but ran only six seasons, Doctor Who has sustained compelling storytelling over 39 seasons—a 550% longer legacy.