Toclafane

“The Toclafane” was the name given by Prime Minister "Harold Saxon” to a race of supposed benevolent creatures who wanted to start diplomatic relations with Earth. In reality, “Saxon” was the Master and the so-called “Toclafane” were actually sadistic killer cyborgs that represented the final form of the human race, integrated into spherical, floating, mechanical shells. (TV: Last of the Time Lords) The name "Toclafane" was given to them by, after a fairy tale monster from Gallifrey, the local equivalent of Earth's "Boogeyman". (TV: The Sound of Drums)

Biology
The Toclafane were cyborgs used as the Master's brawn and muscle when taking over Earth. They were 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 had 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 an enjoyment in killing their great ancestors because "it's fun". (TV: Last of the Time Lords)

Each Toclafane had built-in life-support and teleportation systems. The shells were capable of flight and were fast and manoeuvrable, and could survive the harsh climate and temperature of space with no side-effects. Concealed within the shell were extendable razor-sharp blades and spikes, used as their up-close-and-personal weaponry. The spheres were also equipped with red laser guns that could disintegrate life forms. (TV: The Sound of Drums) The spheres could be shot down by an electrical surge of 58.5 kiloamperes, with a transferred charge of 510 megajoules precisely. Man-made electrical barriers could be constructed to sustain the right energy level balance needed to 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. (TV: Last of the Time Lords)

The Master's minions
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, essentially cannibalising themselves and regressing to children. Even so this was not enough, as the universe was still collapsing around them and they had no where else to go.

, using the Doctor's TARDIS, travelled to the planet in the year 100,000,000,000,000 where he met them. Over time, he became master over them and devised a plan to enable them to change history and survive. He soon saw them as his "children". (TV: Last of the Time Lords)

Invasion of Earth
As Prime Minister of Great Britain, the Master announced he had made contact with a race of friendly aliens who offered wisdom, technology and protection in return for humanity's friendship. 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 history. (TV: The Sound of Drums) With the Toclafane, the Master built the beginnings of a new Time Lord Empire with the army of six billion Toclafane. (TV: Last of the Time Lords)

The Toclafane invasion was a success and the Master ordered the Toclafane to remove one tenth of the population of Earth. (TV: The Sound of Drums) They then subjugated humanity and forced them to build a fleet of 200,000 rockets to take over the rest of the universe. Their plans were thwarted one year after the invasion by the Doctor and his associates. Jack Harkness destroyed the paradox machine with an assault rifle. The machine's destruction reversed time to the moment it was activated, just after the US President was killed and just before the Toclafane arrived. Humanity, aside from those on the Valiant, did not remember they had been invaded. (TV: Last of the Time Lords)

Legacy
A Toclafane ended up in the Verbier Museum of the Impossible. (PROSE: Canaries)

One source suggested a link between the Toclafane and the Quarks after questioning whether the Quarks truly were robots. The authors noted the Quarks were known for childlike voices, glee at causing havoc, and small size. Indeed, the head of the Quarks resembled the sphere design of the Toclafane. (PROSE: The Monster Vault)

Behind the scenes

 * Russell T Davies came up with the original design and idea for the Toclafane in 2004, and briefly considered forcing Robert Shearman to use them as a replacement for the Dalek in a proposed series 1 story that would have been entitled Absence of the Daleks, 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.
 * Absence of the Daleks would have established that mysterious spheres from the future, who would later be revealed to be humans, had attacked the Time Lords among all other sentient species they could find, with the Nestenes and the Daleks among the civilisations decimated. Ultimately, the Time Lords trapped the spheres on Gallifrey, where they sacrificed themselves in an act of mutually assured destruction to eliminate the spheres, leaving only the Ninth Doctor and one known surviving sphere, which became the Metaltron. (The Dalek Handbook)
 * Revived for use in the series 3 finale, the "Future Human" concept was initially named "Roclafane", but was later renamed to Toclafane to avoid the potential mistaken belief that they were simply Racnoss who listened to too much rock music. (DWMSE 17)
 * In the story of Doctor Who: Legacy, the Toclafane return as time travelling Sontarans launch attacks throughout history. Appearing at almost every Sontaran outpost throughout the continuum, the Toclafane overrun Sontar in a cull witnessed by the unfamiliar First Doctor, who describes them as "metal spheres". Bringing the Sontaran army under their control, the Toclafane follow, who orders them to find the Doctor.