10 Horrific Fates Suffered By Doctor Who Characters
6. The Entire Human Race Turns Into Robotic Killing Machines (Last Of The Time Lords)
The Master's personal hench-bots, we first meet the Toclafane in Series 3's The Sound of Drums, where all we really learn about them is that they're billions in number, and that they're very adept at murdering people with an assortment of lasers and blades.
Their uninspired spherical design and lack of a compelling motivation made them a serviceable villain at best, but everything changed in followup episode Last of the Time Lords, where, in a shocking twist, we learned the truth behind their creation.
The supposedly alien Toclafane were actually human beings from billions of years in the future, with their heads stuffed inside metal balls, reduced to nothing but wires and machinery. The Toclafane were what became of the last of humanity.
The saddest thing about this fate is that these future humans thought they were headed for a paradise called Utopia, but all that waited for them was darkness, and the cold of a metal shell. How very depressing.