Toclafane

The Toclafane were the final evolution of the human race, cyborgs integrated into spherical, mechanical shells. The name "Toclafane" was given to them by, after a fairy tale monster from Gallifrey, the local equivalent of Earth's "Boogeyman."

Biology
The Toclafane were cyborgs used as the Master's brawn and muscle (he was the brains) when taking over Earth; the heads of humans from the year 100 trillion integrated into a dark-grey sphere-shaped metallic shell, held together with a magnetic clamp. The humans heads have wiring plugged into their wizened heads. The spheres were very little over a foot tall and were sealed shut. They became a hive mind, allowing them to see the destruction of an individual as no threat. Their personality was amoral and childlike from a failed attempt to regress themselves to children; instead having rather primitive emotional traits and like to kill their great ancestors because "it's fun".

The spheres were capable of flight, and could survive the temperature of space, and could survive in it with no side-effects. Concealed within the shell were extendable razor-sharp blades and spikes, use as their up-close-and-personal weapon. A Toclafane could use them to slice up a human being, and would sometimes rotate to cause great harm to their victims. The spheres were also equipped with red laser guns that could disintegrate life forms, typically used as their long range weapon. (TV: The Sound of Drums) The lasers worked like a Judoon blaster, except when the Toclafane fired their disintegrator, it disintegrated a human pretty much within a second of it hitting them, as opposed to the Judoon blaster taking a few seconds to fully disintegrate a target. (TV: Smith and Jones) The spheres could be shot down by an electrical surge of 58.5 kiloamperes, transferred charge 510 megajoules precisely; however, this was most unlikely because this power existed only in lightning bolts and the chances of one bolt striking a Toclafane were extremely low. Man-made electrical barriers, however, could be constructed to sustain the right energy level balance needed for successfully fry the technology incorporated into the Toclafane spheres, rendering them useless and making them drop to the ground, although the human head would still survive. After this, they would demonstrate the ability to be more civilised with people. (TV: The Sound of Drums/Last of the Time Lords)

History
The last of humanity, scattered across the darkness of space, received a message that said "Come to Utopia". Because the Utopia Project was set up to find a way to survive the end of the universe, everyone believed they had found a way. Humans attempted to travel to the mythical paradise, (TV: Utopia) but what they found was a dark, cold and inhospitable world. To survive, the human race "evolved" into the Toclafane.

, using the Doctor's TARDIS, travelled to the planet in the year 100,000,000,000,000 where he met them. As Prime Minister of Great Britain, the Master announced he had made contact with a race of friendly aliens. The Toclafane had tractable, child-like personalities and trusted the Master. The Master had, by this time, converted the TARDIS into a paradox machine, allowing the six billion Toclafane to invade Earth in their own past and change their own past history. Thanks to the machine, the universe did not intervene to alter the paradox of humanity being subjugated by their own descendants. With the Toclafane, the Master built the beginnings of a new Time Lord Empire with the army of six billion Toclafane.

The Toclafane invasion was a success. The Master ordered the Toclafane to remove one tenth of the population of Earth. They subjugated humanity and forced them to build a fleet of 200,000 rockets to take over the rest of the universe. The Toclafane could kill their ancestors without cancelling themselves out due to the paradox machine. Their plans were thwarted one year after the invasion by Jack Harkness, who destroyed the paradox machine with an assault rifle, forcing the Toclafane back to the end of the universe on Utopia. Humanity aside from those on the Valiant and Wilfred Mott did not remember they had been invaded. With the Master's subsequent death preventing the Toclafane from being brought back in time, they were trapped in their future time zone. Their cousins on Malcassairo became extinct when it went nova but the fate of the Toclafane themselves was never clear. (TV: The Sound of Drums/Last of the Time Lords)

Behind the scenes

 * The voices of the Toclafane sound the same as those of the Gelth, due to the use of a team of regular voice artists for aliens (except those voiced by a celebrity guest), many of whom voiced both the Gelth and the Toclafane.
 * Russell T Davies came up with the original design for the Toclafane when he was coming up with a potential alternate creature to use in the episode Dalek, had rights issues to the Daleks not been worked out. This early version was called "Future Human" and Davies' original illustration is included in Doctor Who: The Writer's Tale - The Final Chapter.