"If we're both humans why do you like killing us?...because its fun!"
The Toclafane were the final evolution of the human race in the year 100,000,000,000,000. The name "Toclafane" was given to them by the Master, after a fairy tale monster from Gallifrey, the local equivalent of Earth's "Bogeyman".
They were originally humans who tried to escape the end of the world billions and billions of years into the future. They travelled to Utopia a planet supposed to still be suitable for life, with help from the tenth Doctor, Martha and Captain Jack the last humans went to utopia on their rocket.However Utopia was not as great as they thought it would be, Utopia was a dark wasteland. In order to survive the humans became cyborgs, they put their heads into sphere like floating machines allowing them to live and fly. 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.
Inside the Spheres were lasers and blades capable of killing any human.
The Master, a evil Time Lord travelled to Utopia with the Doctor's Tardis which he stole. He took with him a human female called Lucy which he married. Turing the Tardis into a paradox machine he took all of the Toclafane back to earth. Thanks to the machine, the universe did not intervene to alter the paradox of humanity being subjugated by their own descendents. With the Toclafane, the Master built the beginnings of a new Time Lord empire with the army of six billion Toclafane.The Toclafane killed many humans during their invasion. Their first kill during the invasion was the President of the United States who was supposed to meet the new alien visitors. 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, forcing the Toclafane back to the end of the universe on Utopia. Humanity 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. Although their cousins on Malcassairo became extinct when it went nova it is unknown if the Toclafane where consumed by Utopia's nova or if they escaped it.