John Pengelly was a gold miner in 19th century California. He had a deed allowing him to mine in a certain area of Ajax Creek.
Like the other miners, John was taken over by an alien entity in the gold. It used the miners to help it find its way home. Even though he was possessed, however, John still remembered his family. When the Sixth Doctor found him, John was reciting from memory a letter he had written to his wife. John and the other miners were freed when the Doctor freed all the gold. (PROSE: Whiskey and Water)