Nin

The Nin were a slug-like peace-loving alien species whose home world was destroyed by solar flares. They bought the planet Earth from someone called the "King of Earth" (actually a young boy who was using a handheld alien device), not realising that it was not real. Their advanced technology was more than a match for the combination Ssaarg and Hoolox in taking over Earth's. After the Tenth Doctor contacted the owner of the device which caused the problem, the owner, who was an intergalactic estate agent, found suitable homes for the Nin and the others. (COMIC: The Day the Earth Was Sold, The King of Earth)