Which of the following served as the Secretary-General of the United Nations?

Javier Perez de Cuellar served as the Secretary-General of the United Nations. Javier Perez de Cuellar was a Peruvian diplomat and served as the fifth Secretary-General of the United Nations from 1982 to 1991. He was the first Secretary-General from a developing country, and he oversaw several key events during his tenure, including the Iran-Iraq War, the Soviet war in Afghanistan, and the end of the Cold War. As Secretary-General, Perez de Cuellar worked to promote peace and security in various parts of the world, including Central America, the Middle East, and Africa. He also played a crucial role in resolving conflicts in Namibia and Cambodia. After leaving the United Nations, Perez de Cuellar continued to be involved in international diplomacy and conflict resolution, and he was recognized for his contributions to world peace and security. Therefore, Javier Perez de Cuellar served as the Secretary-General of the United Nations.