- Video report by ITV News Political Reporter Daniel Hewitt
Kofi Annan, the former secretary-general of the United Nations, had died at the age of 80, his family announced.
He was awarded the Nobel Peace Prize, jointly with the UN, in 2001, for his work reforming the organisation and for fighting for human rights.
His family said he "was a global statesman and a deeply committed internationalist who fought throughout his life for a fairer and more peaceful world".
He passed away in Switzerland "after a short illness", the family said in a statement.
Mr Annan spent virtually his entire career as an administrator in the UN.
He served two terms as secretary-general from January 1997 to December 2006.
Challenges from the outset forced him to spend much of his time struggling to restore its tarnished reputation.
His enduring moral prestige remained largely undented, however, both through charisma and by virtue of having negotiated with most of the powers in the world.
When he departed from the United Nations, he left behind a global organization far more aggressively engaged in peacekeeping and fighting poverty, setting the framework for the U.N.'s 21st-century response to mass atrocities and its emphasis on human rights and development.
"Kofi Annan was a guiding force for good," current UN secretary-general Antonio Guterres said.
- Gordon Brown pays tribute to Kofi Annan
Even out of office, Annan never completely left the U.N. orbit. He returned in special roles, including as the U.N.-Arab League's special envoy to Syria in 2012.
He remained a powerful advocate for global causes through his eponymous foundation.
Annan took on the top UN post six years after the collapse of the Soviet Union and presided during a decade when the world united against terrorism after the Septmeber 11 attacks.
He argued against the invasion of Iraq in 2003 by the US and the UK, saying it should not happen without UN backing.
Mr Annan is survived by his wife and three children.