Tom (Corner of the Eye)
Tom was an agoraphobic man living in England during the 21st century.
He was stalked by a Floof, who commonly caused mischief in his house, moving objects and hiding things. His wife, Kathy, was killed by the Floof, who hid the body in the basement. Tom noticed the Floof for a brief second while shaving, and when looking back over photos of his life noticed him throughout the background.
After Tom met the Tenth Doctor, he was told about the Floof and what it had done to his wife. The Floof had manipulated Tom into thinking that he spoke to her every day on Instant Messenger, when in fact Tom had no internet connection and it was an AI program all along. After the truth was revealed, the Doctor chose to take Tom away from the Floof, but Tom still felt responsible for the Kathy AI, feeling he could not leave her alone.
While he would have stayed for the real Kathy, Tom eventually acknowledged he needed to leave, so he and the Doctor had the Floof create an AI of Tom to keep Kathy's AI company forever, and the real Tom left the house with the Doctor. (PROSE: Corner of the Eye)