Diggers were once the inhabitants of the Underland region that housed Regalia. Bartholomew of Sandwich declared war on them. Sandwich poisoned their water supply when war threatened to fail. This is how the humans got the name "killers" in the Underland and why many feared them. Most diggers were thought to have died and only few to escape, but that none survived. However, there were still some that survived. In The Code of Claw, the diggers sided with the Bane to get revenge on the humans. They are described to look like star nosed moles that are seen in the Overland, and Gregor even recalls seeing one at the family farm in Virginia.