Toclafane
From Tardis Wiki, the free Doctor Who reference
The Toclafane were fairy tale monsters from Gallifrey, their name, like the Bogeymen on Earth, just made up.
In 2008, the Master claimed to have contacted the Toclafane (in reality a race of Human-based cyborgs) and, using a paradox machine linked to the Doctor's TARDIS, allowed the entire race to pour through to decimate the Human population and create a Time Lord Empire. (DW: The Sound of Drums / Last of the Time Lords)
Behind the Scenes
The Toclafane were based on V.I.N.CENT from the Walt Disney film The Black Hole, who looks a bit similar but has a much more friendly personality.