Kofi Annan will be remembered for the way he drew attention, over and over again, to the plight of those caught up in war, environmental disaster, or simply grinding poverty.
The way he quietly but firmly reminded world leaders, however powerful, that they needed to put their duty to their citizens above their political careers.
World figures have been paying tribute to former UN secretary-general and Nobel laureate Kofi Annan, who has died at the age of 80.
Current UN chief Antonio Guterres hailed him as "a guiding force for good" and Russian President Vladimir Putin described a "remarkable person".
Ex-US President Barack Obama said Annan had always pursued "a better world".
The Ghanaian national served as UN chief from 1997 to 2006 and is the only black African ever to hold the post.
Since then he has served as the UN special envoy for Syria, leading efforts to find a solution to the conflict.
Remembering the world's top diplomat
Obituary: Kofi Annan
The career diplomat died in hospital in the Swiss city of Bern. He had been living near Geneva for several years.
He "passed away peacefully on Saturday after a short illness", the Kofi Annan Foundation said.
He was a "deeply committed internationalist who fought throughout his life for a fairer and more peaceful world", the statement added.
UN high commissioner for human rights Zeid Ra'ad Al Hussein said in a tweet he was grief-stricken over Annan's death.
Mr Obama, the first African American to win the White House, said: "Long after he had broken barriers, Kofi never stopped his pursuit of a better world."
President Putin said the memory of Annan would "forever live in the hearts of Russians".
Meanwhile, Indian PM Narendra Modi said "the world has lost not only a great African diplomat and humanitarian but also a conscience keeper of international peace and security".