"We've lost our greatest son," South African President Jacob Zuma said in announcing Mandela's death, which occurred at 8:50 p.m. at Mandela's home in the Johannesburg suburb of Houghton.
"Like so many around the globe, I cannot fully imagine my own life without the example that Nelson Mandela set. And so long as I live, I will do what I can to learn from him," Obama said of the man whom he met only once, in Washington in 2005. Mandela was too ill to receive visitors during the president's June visit to Africa.
U.N. Secretary-General Ban Ki-moon called Mandela "a singular figure on the global stage -- a man of quiet dignity and towering achievement, a giant for justice and a down-to-earth human inspiration."
British Prime Minister David Cameron sent condolences via Twitter: "A great light has gone out in the world. Nelson Mandela was a hero of our time. I've asked for the flag at No10 to be flown at half mast."
No. 10 is the address of the prime minister's official residence in London.
Former President Clinton, whose presidency coincided with Mandela's historic evolution from political prisoner to head of state, lamented the loss of "one of [the world's] most important leaders and one of its finest human beings."
On Capitol Hill, politicians from both sides of the aisle were united in lauding the revered freedom fighter as a man who transformed not only South Africa but also the world.
"Nelson Mandela taught us about humanity in the face of inhumanity, and left an unjust world a more just place," said Sen. Robert Menendez, the New Jersey Democrat who chairs the Senate Foreign Relations Committee. "He ended apartheid and united a nation, while demonstrating almost supernatural gifts of inner strength, forgiveness and reconciliation. Few individuals in human history can truly claim a legacy of peace and perseverance like Mandela can."
Former Republican presidential candidate Mitt Romney, in a tribute posted on Twitter, hailed Mandela as "an unsurpassed healer of human hearts."
"It is hard to overstate Nelson Mandela's transformative impact on his country and the world," said U.S. Sen. Chris Coons, the Delaware Democrat who chairs the Senate Foreign Relations subcommittee on African affairs. "The lesson of his personal determination in the face of decades of imprisonment and oppression, followed by his unwavering grace and forgiveness towards his former captors, is one of the great reconciliation stories in human history."
New York City Mayor Michael R. Bloomberg recalled the ticker-tape parade organized in his city for Mandela in 1990, the year he was released after 27 years of imprisonment for challenging white rule in South Africa, as well as Mandela's visit after the terrorist attacks on Sept. 11, 2001.
"Today, we lost one of the most transformative and influential figures in modern history. Nelson Mandela was a global icon who broke the back of apartheid in South Africa and inspired generations of people around the world with his spirit of resolve and reconciliation," Bloomberg said.
Australian Prime Minister Tony Abbott said in a radio interview that "Nelson Mandela was one of the great figures of Africa, arguably one of the great figures of the last century."
Archbishop Desmond Tutu, like Mandela a Nobel Peace Prize laureate, wrote a tribute to his fellow South African rights champion on the AllAfrica website in which he said all the world mourned the loss of "a colossus of unimpeachable moral character and integrity, the world's most admired and revered public figure."