The Unlived

The Unlived were beings from potential times that could have happened, but which didn't, in any timeline. As described by the Lady, they were killers full of hate for everything.

They were able to enter N-Space through a gap between time and space to their own dimension, which allowed them to invade. Their leader, Skaul, along with a group of Unlived, took over a ship and attempted to kill all living beings in the universe. He sought Leela and her people as they were killing his people. He gave the Dalek Time Strategist an ultimatum to help their cause or die, which the Daleks rejected, causing a battle between the two species. Through this battle, the Unlived were able to obtain Dalek weaponry.

After the War Doctor began closing the entrance to their dimension, the Unlived returned to it to defend it, only to be all killed as the entrance was closed for good. (AUDIO: The Lady of Obsidian)