The main figures in the founding of the United Nations include Franklin D. Roosevelt, who was President of the United States and a strong advocate for international cooperation, and Winston Churchill, the British Prime Minister. Additionally, representatives from 50 countries signed the UN Charter in San Francisco in 1945, including prominent figures like Eleanor Roosevelt, who played a crucial role in drafting the Universal Declaration of Human Rights. The UN was established to promote peace, security, and cooperation among nations following the devastation of World War II, aiming to prevent future conflicts.