The Quoll were shapeshifters from the Reft Sector.
After eating the Reft Sector bare, they travelled to other planets in search of food. One Quoll named Gevaunt landed on the human colony Kolpasha and disguised himself as a human.
Since the Quoll could not consume humans, Gevaunt planned to turn the humans into edible material by getting them addicted to the Eternal Youth Drug. However, Gevaunt was killed by the Fourth Doctor before he could carry out his plans. (COMIC: Victims)