Solution:The "Big Three" who played a lead role in designing the new organizationthe United Nations-were the Soviet Union, the United States of America, and the United Kingdom.
These three major Allied powers during World War II were instrumental in shaping the post-war world order, including the establishment of the UN itself.
Their leaders, Joseph Stalin, Franklin D. Roosevelt, and Winston Churchill, respectively, were key figures in the negotiations that led to the creation of the United Nations.