Doctor Who: 10 Major Ways The Doctor Affected Human History
2. Starting The Great Fire Of London
The Doctor and starting fires. An inseparable duo.
The Visitation is a Fifth Doctor historical that included an explanation for how - within the Doctor Who universe, at least - the Great Fire of London was started.
In the fourth part of this serial, the Doctor tracks down the Terileptils, a reptilian alien species that we haven't seen in a TV story since the 1980s. Finding their base in London, the Doctor proceeds to confront them, all the while carrying a burning torch with him. You can see where this is going.
Sure enough, the Doctor drops his torch into a pile of hay, and the resulting fire spreads to a nearby Terileptil weapon, which explodes due to the heat. The fire then grows and spreads, and the Doctor just... flies off.
Umm... excuse me, but this was your fault! Doesn't the TARDIS have a hose pipe or something? Can't you pour out the swimming pool?
At the end of the story, it's revealed that the fire was started in a bakery on Pudding Lane, and so the Doctor knew that it was the beginning of the Great Fire of London. By leaving, he left history to play out as it was always meant to.