Halldon

The Halldons were a race of powerful beings.

History
On Ollendorf 2, the Doctor discovered the unpublished writings of a human scientist, Bryant Anderson, next to Anderson's own corpse and the remains of a Dalek. The papers revealed that shortly before his death, Anderson had discovered the true origin of the Daleks. In ancient times, the Halldons, as part of a scientific experiment, had transplanted Earth humans to the barren planet Ameron and artifically accelerated their evolution. Within two hundred years, the Halldons' test subjects had advanced to such an extent as to build fearsome weapons which frightened even their Halldon masters.

Realizing the experiment was spinning out of control, the Halldons attempted to wipe out the Ameron humans, only for them to defend themselves and retaliate to the point of completely exterminating the Halldons. Free to advance unhindered, the evolved humans, determined to ensure their own survival, continued to evolve and eventually became the Daleks whom the Earth humans feared so greatly. (PROSE: We are the Daleks!)

The Halldons engaged in a temporal skirmish with the Eternals, which ended with the Time Lords stepping in to put an end to the universe-threatening hostilities. According to one account, this was one of the only two time wars in which the Time Lords had engaged before the start of their Great Time War with the Daleks themselves, which would end in their destruction. (PROSE: Meet the Doctor)

Behind the scenes
Doctor Who: Monsters and Villains claims that the Halldons were the ancestors of the Brothers of Hame, who created the Forest of Cheem, initially mentioned in Meet the Doctor as one of the "higher species" who were aware of, and wept at the sight of, the Great Time War.