John Scanlon was someone who managed to acquire a time ship and used it to, according to himself, change Earth's history to prepare it for an alien invasion in his own time, which was two thousand years in Edward Grainger's future. He travelled back in time to 1936.
However, Scanlon also stole valuable artefacts from Earth's history, justifying it because he was trying to save Earth's future. He also had photographs taken of King Edward VIII and Wallis Simpson, months before the photos should have been available. Grainger, working for the British government, was able to defeat Scanlon with the help of the Fifth Doctor and Peri Brown. (PROSE: The Church of Football)