Patrick Rix was a Scottish doctor.
He became insane when his deformed child Stephen's birth caused his wife's death. He conducted research on homeless people to find the source of human pain. He was driven out of Edinburgh in disgrace when his experiments were uncovered.
When he was transported into Galah's TARDIS and could not escape the creatures attacking him there, he took his own life. This unintentionally allowed him access to the subroutines of the TARDIS, allowing him to control it to a great extent. The Seventh Doctor and Galah were able to give him visions that forced him to face the horrible things he had done. The two Time Lords were then able to erase his personality from the TARDIS. (PROSE: Strange England)