His foundation announced his passing on Saturday in Switzerland, saying he died of an unspecified illness at 80.
“Wherever there was suffering or need, he reached out and touched many people with his deep compassion and empathy,” the foundation said in a statement.
Annan spent virtually his entire career as an administrator in the United Nations.
He became the first secretary-general to be hired from withing. He served two terms, Jan. 1, 1997, to Dec. 31, 2006, capped nearly mid-way when he and the UN were jointly awarded the Nobel Peace Prize in 2001.