“And now I know you're mad, I just wanted to make sure."
The Doctor has fought many mad scientists among whom are the worst humanity has to offer, others are simply misguided or blinkered by their own fanaticism, usually it leads to their deaths. Here's the run down on my top ten, which goes up to eleven. Because that's mad/I couldn't choose which to leave out/it's the standard set by the BBC iPlayer volume control.
5. Taren Capel
Brilliant politician and scientist, very highly respected for his work improving agriculture and tackling world hunger. But in secret he was a madman hell bent on taking over the world. He murdered people behind the scenes replacing them with various accomplices and moved himself into a position of power. His ultimate aim was to subjugate the entire world with the threat of destruction using his control over volcanoes and earthquakes.