Mr Cotterill was created by Annette Billingsley as the villain in her thirty-two book series of The Troubleseekers children's novels. He was one of four smugglers who stole chests of gold. He hid three out of four of the chests and after he got out of prison, he faked his death and pretended to be a caretaker while he secretly searched for the last chest that his fellow smugglers had hid. To cover up his activities, he put lanterns on pulleys in the woods to make people think ghosts were there and scare them away.
In a world created by fictional books Martha Jones had read, Martha and the Tenth Doctor spoke to Mr Cotterill, who was actually a Ch'otterai in disguise. (PROSE: The Mystery of the Haunted Cottage)