Mandela spent 27 years in prison under South Africa's segregationist apartheid regime. As international awareness of South Africa's racial discrimination grew, Mandela became one of the world's most famous prisoners.
Mandela served a single five-year term and stepped down voluntarily to focus on charity work.
Though apartheid is in the distant past, racial disparities and injustices remain. Machel said South Africans should continue to work for greater racial and ethnic reconciliation to honor Mandela's legacy.
U.S. President Barack Obama and wife Michelle said that the world lost a leader one year ago "whose struggle and sacrifices inspired us to stand up for our fundamental principles, whose example reminded us of the enduring need for compassion, understanding, and reconciliation, and whose vision saw the promise of a better world."