1. David Lloyd George: He served as the Prime Minister of the United Kingdom from 1916 to 1922. He is widely regarded as one of the most important figures of the war, as he led Britain to victory.
2. Georges Clemenceau: He was the Prime Minister of France from 1917 to 1920. Clemenceau was known as "the Tiger" for his fierce determination to win the war.
3. Woodrow Wilson: He served as the President of the United States from 1913 to 1921. Wilson initially kept the US neutral but eventually joined the war in 1917. He played a significant role in the peace negotiations that followed the war.
4. Kaiser Wilhelm II: He was the Emperor of Germany from 1888 to 1918. He was a major figure in the war as Germany was one of the main belligerents.
5. Tsar Nicholas II: He was the Emperor of Russia from 1894 to 1917. Nicholas was forced to abdicate in 1917 during the Russian Revolution, which led to Russia's withdrawal from the war.
These are just a few of the many leaders who played important roles during World War I. The war was a truly global conflict, involving more than 30 countries and affecting the lives of millions of people around the world.