Doctor Who: 10 Major Ways The Doctor Affected Human History

While the Doctor often plays with time like it's a big ball of string, they do at least have some restraint when it comes to fixed points.

Certain events - like the eruption of Vesuvius - must always happen, so they can't really go and change them, even if they want to. But what they can do is get involved in making those fixed points happen.

Series 4's The Fires of Pompeii offers up a devastating example of this, with the Tenth Doctor and Donna becoming embroiled in a fiery alien plot to conquer the Earth.

This culminates with the Doctor having to make a difficult choice: he can either let the aliens do their thing, or he can stop them by blowing up Vesuvius and killing them, which will also destroy Pompeii in the process.

With a little help from Donna, he chooses the latter, unleashing the volcano's fury upon the thousands of innocent people below.

This was the lesser of two evils for sure, but watching the Doctor wrestle with this decision is haunting, and it makes you wonder what other hugely destructive events the character has been unknowingly involved in over the centuries.