Fliant Wormbleeder was an intergalactic estate agent. At one point, he lost his handheld device on Earth, which a young boy named Robbie found. Thinking it was just a game console, Robbie unintentionally gave the ownership of the Earth to three different alien races, the Nin, Ssaarg and Hoolox.
When the Tenth Doctor found the source of the transmission of the King of Earth, he took the device from Robbie and called the owner. The owner appeared as a hologram and looked through his catalogue to find suitable homes for the three alien races. (COMIC: The Day the Earth Was Sold, The King of Earth)