Donald Trump

Donald Trump was an American politician the youth of 2016 considered to be unstoppable. (PROSE: What She Does Next Will Astound You)

Behind the scenes
In DWM 503, Steven Moffat answered the question, "What does the Doctor make of Donald Trump's decision to run for President of the United States?" Moffat replied that "although the Doctor normally takes no part in politics, he is disgusted and turbulent with rage" and went on to say that the Doctor has seen a parallel universe in which Trump won the election and the world was plunged into "certain doom".

In the real world Donald Trump was elected United States President on 9 November, 2016.