There have been many leaders (Monarchy and Parliamentary) in the long history of Britain. During the second World War, Winston Churchill was the Prime Minister that helped Britain and her allies, stand against Nazis Germany.
During World War II, the 'Big Three' nations who were allied against the Axis powers were Great Britain, the Soviet Union, and the United States. Numerous other nations, small and large, were associated with these leaders in the world war.
The Allied leaders were Soviet union- Joseph Stalin, USA- Franklin Delano Roosevelt, and Winston Churchill for Great Britain. The Axis leaders were Germany - Adolph Hitler, Italy - Benito Mussolini, and Empire of Japan - General Tojo.
Winston Churchill was Prime Minister of Great Britain during most of World War II and as such was one of the leaders of the Allies. The Axis was the name given to the enemy led by Germany and Adolf Hitler.