I know Churchill was a big part of winning the war but what specific events lead to this? I was curious because I recently discovered BBC's list of the most important Britons and expected maybe Newton or Shakespeare at the top but I found Churchill there. So, what lead to him being the most important Briton?
Just for context the BBC list was based on a televised poll of the public, so it's not an historical judgement (although I'm sure if you polled historians you might well get the same result.)
So the answer will almost certainly be for what is most popularly known for, i.e. leading the British (and to an extent the world) through World War II. In that sense this is really a question about contemporary British public opinion than it is about Churchill's historical achievements.
That's as opposed to some of the things that each of us in our respective fields might site him for as being interesting, for example his role in post-World War I Middle East policy in my particularly area of study.