Final answer:
The main leaders present at the Yalta Conference in 1945, often referred to as the "Big Three", were Franklin D. Roosevelt, Winston Churchill, and Joseph Stalin.
Step-by-step explanation:
The main leaders present at the Yalta Conference in 1945, often referred to as the "Big Three", were Franklin D. Roosevelt, Winston Churchill, and Joseph Stalin. They were the leaders of the United States, the United Kingdom, and the Soviet Union respectively.