The historical figure famous for diplomacy and contributions to international relations in the 20th century is Kofi Annan, the seventh Secretary-General of the United Nations. Serving from 1997 to 2006, Annan worked to reform the UN, focusing on peacekeeping, human rights, and sustainable development. His efforts in addressing global issues like HIV/AIDS, the Iraq War, and humanitarian crises were instrumental in shaping international policy. Annan was awarded the Nobel Peace Prize in 2001 for his work, solidifying his legacy as a leader committed to promoting peace and understanding among nations during a critical time in global affairs.