The key figure behind the creation of the United Nations was U.S. President Franklin D. Roosevelt. His vision for a post-World War II international organization aimed to prevent future conflicts and promote peace, cooperation, and humanitarian efforts globally. Roosevelt envisioned the UN as a platform where nations could address their grievances diplomatically. This vision was realized in 1945 when the UN was officially established, shortly after Roosevelt's death. His contributions, along with those of other leaders like Winston Churchill and Charles de Gaulle, helped shape the UN's structure and purposes, fostering global collaboration and dialogue.