The prominent figure associated with the founding of the United Nations is Franklin D. Roosevelt, the 32nd President of the United States. Roosevelt played a crucial role in envisioning a post-World War II organization aimed at promoting international cooperation and preventing future conflicts. His leadership during the war and his advocacy for collective security laid the groundwork for the UN's establishment in 1945. Roosevelt's vision emphasized the principles of human rights, peace, and multilateral diplomacy, which continue to be foundational pillars of the organization.