Annan died in a hospital in Bern, Switzerland. Reuters reported.
Annan was the seventh Secretary-General, serving from 1997 to 2006. He shared the Nobel Peace Prize in 2001 with the United Nations for "for their work for a better organized and more peaceful world," CNN reported.
Annan was born in Kumasi, Ghana, on April 8, 1938. He was a member of The Elders, a group of global leaders working for human rights that was founded in 2007, CNN reported. He became the organization's chairman in 2013.
In a tweet, the UN Migration Agency noted that "Today we mourn the loss of a great man, a leader, and a visionary."
Annan was the first black African to fill the role of the world's top diplomat, the BBC reported. He later served as the UN's special envoy for Syria, leading efforts to find a peaceful solution to the volatile area of the Middle East.
During Annan's tenure as Secretary-General, the Berlin Wall was dismantled, al-Qaeda conducted terrorist attacks in the United States on Sept. 11, 2011, and the United States invaded Iraq, The New York Times reported.
UN Secretary-General António Guterres said Annan "was the United Nations," The Guardian reported.
“He rose through the ranks to lead the organisation into the new millennium with matchless dignity and determination,” Guterres said.
Annan joined the United Nations in 1962 as an administrative officer with the World Health Organization, The Guardian reported. Annan later served with the Economic Commission for Africa, the UN Emergency Force in Ismailia and the UN high commissioner for refugees in Geneva, the newspaper reported.
Before becoming secretary general, Annan was under-secretary general for peacekeeping. He also served as a special representative of the secretary general to the former country of Yugoslavia in 1995 and 1996, according to The Guardian.