Light has gone out in the world: PM
David Cameron led tributes to South Africa's first black president Nelson Mandela, saying "a great light has gone out in the world".
The flag at No 10 will be flown at half-mast in honour of the former leader, who was a "hero of our time", the Prime Minister said.
Mr Cameron said: "A great light has gone out in the world. Nelson Mandela was a towering figure in our time; a legend in life and now in death - a true global hero.
"Across the country he loved they will be mourning a man who was the embodiment of grace.
"Meeting him was one of the great honours of my life. My heart goes out to his family - and to all in South Africa and around the world whose lives were changed through his courage."
MPs will be given the opportunity to pay tributes to Mr Mandela in the House of Commons on Monday, he added.
Former prime minister Tony Blair said the political leader was a "great man" who had made racism "not just immoral but stupid".
"He was a unique political figure at a unique moment in history," he said.
"Through his leadership, he guided the world into a new era of politics in which black and white, developing and developed, north and south, despite all the huge differences in wealth and opportunity, stood for the first time together on equal terms.
"Through his dignity, grace and the quality of his forgiveness, he made racism everywhere not just immoral but stupid; something not only to be disagreed with, but to be despised. In its place he put the inalienable right of all humankind to be free and to be equal.
"I worked with him closely, and remember well his visits to Downing Street. He was a wonderful man to be around, with a sharp wit, extraordinary political savvy and a lovely way of charming everyone in a building.
"He would delight in making sure that the person on the door or serving the tea would feel at home with him and be greeted by him with the same kindness and respect he would show a leader. So the warmth of his personality was equal to the magnitude of his contribution to the world.
"He was a great man, a great leader and the world's most powerful symbol of reconciliation, hope and progress."
Labour leader Ed Miliband called his work to unite South Africa in the face of personal hardship and oppression "extraordinary".
He said: "The world has lost the inspirational figure of our age. Nelson Mandela taught people across the globe the true meaning of courage, strength, hope and reconciliation.
"From campaigner to prisoner to president to global hero, Nelson Mandela will always be remembered for his dignity, integrity and his values of equality and justice.
"He was an activist who became president and a president who always remained an activist. Right to the end of his life he reminded the richest nations of the world of their responsibilities to the poorest.
"Above all, he showed us the power of people, in the cause of justice, to overcome the mightiest obstacles. He moved the world and the world will miss him deeply.
"During the struggle against apartheid, the Labour Party was proud to stand with the people of South Africa in solidarity. Today we stand with the people of South Africa in mourning."
Foreign Secretary William Hague also paid tribute to Mr Mandela, saying: "It was with great sadness that I learned of the death of Nelson Mandela.
"Nelson Mandela was one of the greatest moral and political leaders of our time. His life story is a compelling and inspiringly profound political journey.
"An international icon and inspiration to millions, his appeal transcended race, religion and class. He was at once a leader of immense character and strength, and a man closely attuned to the needs of his people.
"Nelson Mandela once wrote, 'I don't think there is much history can say about me.' Yet he will be remembered forever for his lifelong fight against racial oppression, not least during his 27 years of incarceration, and as the first freely elected leader of a multi-racial South Africa.
"His name will echo down the ages for his immense contribution to his country, to Africa, and to the world, and his tireless work for peace and reconciliation. He set a powerful example to us all of sacrifice and enormous fortitude. His courage, humility and sense of forgiveness have secured his place in history.
"He will be greatly missed across the world."
American civil rights leader Rev Jesse Jackson said Mr Mandela's "imprint" would be "everlasting".
"My heart weighs heavy," said Mr Jackson, who has been in the UK this week and spoke to students in Cambridge on Monday. "The imprint he left on our world is everlasting."
He added: "Nelson Mandela was a transformational figure; to say he was a 'historical figure' would not give him his full due.
"My heart burst with excitement on that day of Mandela's release from Victor Verster Prison, 11 February 1990. When word got out about his impending release, maids started doing the toya toya in the hallways, beating pots and pans, weeping and demonstrating."
Mr Jackson said he had been at Mr Mandela's presidential inauguration. "We forged an everlasting relationship," he said. "We've met numerous times in South Africa - the last time in 2010 where we spoke about boxing, sports, politics, and traded baseball caps.
"Nelson Mandela was a giant of immense and unwavering intellect courage and moral authority. He chose reconciliation over retaliation. He changed the course of history.
"Now, both South Africa and the US, have unfinished business to complete. Mandela is not gone, he remains with us always. He'll always be a chin bar to pull up on. Mandela has indeed forged South Africa as a new 'beauty from ashes'.
"He has left this earth, but he soars high among the heavens, and his eloquent call for freedom and equality is still heard amongst the winds and the rains, and in the hearts of the people the world over."
Former US president Bill Clinton said last night: "Today the world has lost one of its most important leaders and one of its finest human beings. And Hillary, Chelsea and I have lost a true friend.
"History will remember Nelson Mandela as a champion for human dignity and freedom, for peace and reconciliation.
"We will remember him as a man of uncommon grace and compassion, for whom abandoning bitterness and embracing adversaries was not just a political strategy but a way of life.
"Our thoughts and prayers go out to Graca and his family and to the people of South Africa. All of us are living in a better world because of the life that Madiba lived.
"He proved that there is freedom in forgiving, that a big heart is better than a closed mind, and that life's real victories must be shared."
In a statement released through NBC News, former US president George Bush said: "President Mandela was one of the great forces for freedom and equality of our time. He bore his burdens with dignity and grace, and our world is better off because of his example.
"This good man will be missed, but his contributions will live on forever. Laura and I send our heartfelt sympathy to President Mandela's family and to the citizens of the nation he loved."
Microsoft tycoon and philanthropist Bill Gates said he was honoured to meet Mr Mandela a number of times.
"We left each visit inspired and more optimistic about the opportunity to improve the lives of the poor throughout the world," he said. " From prisoner to president, Nelson Mandela was tireless in his pursuit of equality and justice for all people.
"President Mandela was a remarkable example to us, to our foundation, and to the whole world thanks to a life imbued with courage, dedication and compassion.
"Our thoughts and prayers are with Graca Machel and President Mandela's family. We join with the people of South Africa in grieving the loss of this extraordinary and inspirational leader."
Former prime minister Gordon Brown called Mr Mandela " the greatest leader of our generation", saying he was "a leader of magnanimity, fortitude, unshakeable optimism and most of all, the most courageous man I ever met".
Mr Brown added: "True courage requires not only strength of will but strength of belief. What motivated Nelson Mandela and drove him to risk his life for freedom was a burning passion that irrespective of colour, race and background, all people are created equal - and his list of historic achievements starts with a multiracial South Africa.
"Every accolade in the world was awarded to him but the one he prized most was Children's Champion. As he said in his book, he had climbed one mountain, but there is another still to climb - dignity for every child. He was the greatest of Africans."
The Archbishop of Canterbury, the Most Rev Justin Welby, said: " South Africa has lost its greatest citizen and its father. Nelson Mandela, fighting to the end, is freed to be with his God in joy and reward for his great service and sacrifice...
"We are challenged to show the same degree of humanity, of courage and of generosity."
Deputy Prime Minister Nick Clegg said: "Our thoughts go out to the people of South Africa who will be left heartbroken by this sad news.
"Every so often history produces an individual whose message is universal, and Nelson Mandela will be mourned and missed on every continent around the globe. The hope he offered was enough to unite races. It bridged cultures and transcended generations and it could heal the deepest divides.
"That hope must now live on. Nelson Mandela's legacy will continue to burn brightly, there is little doubt about that. But our greatest tribute to him will be our commitment to equality, humanity and peace - the values for which he very literally put his life on the line."
The United Nations Security Council interrupted a meeting on the tribunals for former Yugoslavia and Rwanda last night and stood for a minute in silent tribute to Mr Mandela.
UN secretary general Ban Ki-moon said he was "a giant for justice" whose "selfless struggle for human dignity, equality and freedom" inspired many people around the world.
"No one did more in our time to advance the values and aspirations of the United Nations," he said.
"Nelson Mandela showed what is possible for our world, and within each one of us, if we believe a dream and work together for justice and humanity. Let us continue each day to be inspired by Nelson Mandela's lifelong example to keep working for a better and more just world."
Baroness (Betty) Boothroyd, the former Commons speaker, fondly recalled the memories about a visit President Mandela made in 1996.
She said: "I welcomed many leaders to Westminster when I was Speaker but he was by far the most remarkable.
"His speech to the joint Houses of Parliament in Westminster Hall in 1996 was a masterpiece of reconciliation after the bitter years of apartheid. He represented 'an outstanding victory of the human spirit over evil', I told him.
"He wrote to me afterwards of his delight at the pomp and ceremony of the occasion and its 'majesty and dignity'. He was especially touched by the Queen's graciousness towards him and the warmth of the British people.
"He was kind enough to add 'It is friends like yourself who have contributed to making our country the democratic rainbow nation we are today'."
London mayor Boris Johnson said: "When the definitive history of our time is written, the name Mandela will stand taller than most - perhaps tallest of them all.
"Nelson Mandela understood the most powerful tool at his disposal was the power of forgiveness. He faced down the tyranny and oppression of apartheid by embracing unity, by rejecting division, by proving without rancour or recrimination that his way was the right way, the best way, and the only way to bring about change.
"Londoners, brought up in a city where the values of diversity and equality were celebrated not suppressed, forged a unique bond with Mandela and the struggle he embodied."
Irish president Michael D Higgins described Mr Mandela as an "immense moral force", saying: "Nelson Mandela is one of history's greatest leaders; a man whose unprecedented courage and dedication broke down the cruel barriers of apartheid in South Africa and led the nation into a new and democratic age."
Irish Taoiseach Enda Kenny said Mr Mandela changed life in South Africa, and humanity.
"As we mark his passing, we give thanks for the gift of Nelson Mandela. We ask that his spirit continues to inspire, guide and enlighten us as we strive to bring freedom and dignity to the family of man, our brothers and sisters, across the world," he said.
"I offer my deepest sympathies, on behalf of the Irish Government and people, to his family, to his friends and supporters, and to the Government and the people of South Africa."
Christian Aid chief executive Loretta Minghella described Mandela as a "man whose strength of vision founded a nation".
"The sufferings and injustices inflicted by apartheid could so easily have led to a reckoning in blood when majority rule was introduced," said Ms Minghella.
"The fact that South Africa's transition from pariah state to independent nation took place in relative peace was largely down to the magnanimity and moral courage of Mr Mandela. "
Amnesty International secretary general Salil Shetty added that his courage "helped change our entire world", and praised his "unswerving resolve" to stamp out racial inequality.
He said: "The death of Nelson Mandela is not just a loss for South Africa. It is a loss for people all over the world who are fighting for freedom, for justice and for an end to discrimination...
"His legacy across Africa, and the world, will stand for generations."
Mohammed Shafiq, chief executive of the Ramadhan Foundation, added: " Whether it was the illegal war in Iraq, the struggle against apartheid or the occupation of Palestine Nelson Mandela never stopped speaking up and for that the world will forever be grateful.
"His legacy will live for generations to come and we give thanks for his life and service. Tonight out hearts are with his family and friends."
World Bank Group president Jim Yong Kim said: "We are deeply saddened to learn of the death of Nelson Rolihlahla Mandela. On behalf of the World Bank Group staff, I convey my deepest sympathies to Graca Machel, Nelson Mandela's family, and the South African people.
"The world has lost a man who brought a rainbow of possibilities to a country that was segregated into black and white."
President of the European Commission Jose Manuel Barroso said: "Mandela changed course of history for his people, country, continent & the world. My thoughts are with his family and people of South Africa."
American civil rights leader Jesse Jackson added that Mr Mandela had been a "rare soul".
"Nelson Mandela was truly a transformative force in the history of South Africa and the world," he said.
"Every now and then a soul of rare vintage comes our way. That by circumstances, sacrifice and suffering, finds its way into the soul of our global culture, the family of man, and calls our better angels to fly.
"Such a soul is Nelson Mandela."
He added: "Imprisoned in Robben Island for 25 years and eight months, Mandela never lost faith that the South African people would win freedom. Suffering breeds character."
David Miliband, president and CEO of the International Rescue Committee, said Mr Mandela's life shows how " personal character, values and personality at the top can make and break nations".
Although he was "brought up to be a bit sceptical of the 'Great Man' theory of history", Mr Miliband said in a blog post: "His passing after a long, arduous, successful and momentous life is rightly an occasion for saluting and celebrating as well as mourning."
He went on: "The campaigns in the 1980s for the West to take some responsibility for change in South Africa seemed so clear to me as a university student urging divestment of college funds from South Africa. In the end, though, the change came from within.
"Nelson Mandela was an example for politicians but also for people, in the way he lived his life and the way he treated others.
"Mandela taught humility, principle, loyalty, endurance, commitment. It somehow seems more poignant to have been able to visit his cell on Robben Island this March while he was still alive."
Mr Miliband said in 2007 he was privileged to sit in Parliament Square in London when a statue of Mandela was unveiled.
"He spoke of coming to London as a young lawyer in the 1950s, and seeing the Victorian generals and politicians commemorated in the square.
"Never did he believe, he said, that he would come back and see the statue of a black man in Parliament Square.
"I am sure there are flowers being laid there now," he said.
Sir Shridath Ramphal, Commonwealth secretary-general from 1975 to 1990, said in a statement: "Tomorrow's children will not be able to say, as we can with pride and a deep sense of privilege, that we lived in the time of Nelson Mandela, a unique and memorable human being.
"'Madiba' has gone from us; but he is part of eternity and will always belong to the entire world. His indomitable spirit will forever inspire people in pursuit of freedom and justice; his humanity will be a beacon for all who are wronged. He made our troubled age less shameful by his own nobility.
"He enriched my own life by the small part I played, as Commonwealth Secretary-General, in restoring him to freedom - even though he showed that truly 'Stone walls do not a prison make, nor iron bars a cage'.
"That my official Commonwealth residence was the one he came to when first he came to London, after his release from prison, to meet those who fought with him against apartheid and the injustices of the apartheid regime, will forever be a badge of honour for the Commonwealth."
Mr Blair told BBC Radio 4's Today programme that Mr Mandela had a good relationship with Britain, despite the opposition to him from parts of the establishment.
"He literally never used to let that bother him at all in terms of his regard for the country and, by the way, he was always perfectly gracious about Mrs Thatcher as well. I think he had a tremendous affection for Britain, he admired it as a country, he liked the people and I know he always used to enjoy coming."
The former prime minister added: "He came to represent something that was much more than just about the resolution of the issues of apartheid and of South Africa, he came to represent something quite inspirational for the future of the world and for peace and reconciliation in the 21st century."
Chancellor George Osborne told Today: "I grew up in the 1980s and the great protest movement of my childhood, the great campaign of my childhood was for the release of Nelson Mandela, so he was very much a backdrop to my life, like the lives of many people listening.
"I think what I remember about him above all is not just his incredible stand for freedom and the endurance of being in prison for so many years but then turning around and reconciling himself with the people who kept him captive and not only did he, as a result, avoid a very bloody civil war in South Africa but I think he stands for something much bigger even than that, which is that there can be hope and reconciliation. I think that's the most extraordinary thing about Nelson Mandela."
U2 frontman Bono, who met Mr Mandela on a number of occasions, said: "It was as if he was born to teach the age a lesson in humility, in humour and above all else in patience.
"In the end, Nelson Mandela showed us how to love rather than hate, not because he had never surrendered to rage or violence, but because he learnt that love would do a better job. Mandela played with the highest stakes.
"He put his family, his country, his time, his life on the line, and he won most of these contests. Stubborn til the end for all the right reasons, it felt like he very nearly outstared his maker. Finally, he blinked. And some of us cry, knowing our eyes were opened to so much because of him."
Former Spice Girl Geri Halliwell, who met Mr Mandela when the group played a charity concert in South Africa, said: " Rip Nelson Mandela, it was a absolute honour to meet such an inspiring man, he was amazing, incredibly charming and warm."
UN secretary-general Mr Ban added today: " Nelson Mandela was 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.
"I am profoundly saddened by his passing. On behalf of the United Nations, I extend my deepest condolences to the people of South Africa and especially to Nelson Mandela's family and loved ones.
"Many around the world were greatly influenced by his selfless struggle for human dignity, equality and freedom. He touched our lives in deeply personal ways. At the same time, no one did more in our time to advance the values and aspirations of the United Nations.
"Nelson Mandela devoted his life to the service of his people and humanity, and he did so at great personal sacrifice. His principled stance and the moral force that underpinned it were decisive in dismantling the system of apartheid.
"Remarkably, he emerged from 27 years of detention without rancour, determined to build a new South Africa based on dialogue and understanding. The Truth and Reconciliation Commission established under his leadership remains a model for achieving justice in societies confronting a legacy of human rights abuses.
"In the decades-long fight against apartheid, the United Nations stood side-by-side with Nelson Mandela and all those in South Africa who faced unrelenting racism and discrimination. His 1994 address to the General Assembly as the first democratically-elected president of a free South Africa was a defining moment.
"The Assembly has declared July 18 , his birthday, Nelson Mandela International Day, an annual observance on which we recognise and seek to build on his contributions to promoting a culture of peace and freedom around the world.
"I was privileged to meet Nelson Mandela in 2009. When I thanked him for his life's work, he insisted the credit belonged to others. I was very moved by his selflessness and deep sense of shared purpose.
"Nelson Mandela showed what is possible for our world and within each one of us - if we believe, dream and work together.
"Let us continue each day to be inspired by his lifelong example and his call to never cease working for a better and more just world."
Queen guitarist Brian May, a founding ambassador of Nelson Mandela's 46664 charity, assisting those infected or affected by HIV/Aids, said: " Very sad to hear of Madiba's passing.
"We (Queen, along with Dave Stewart, and the Corrs) were privileged to spend some days and nights with him at his game park retreat, while we were organising the first 46664 concert for Aids at Green Point Stadium in Cape Town. They were life-changing days, with quiet time and talks around a camp fire at night, which we will remember til we die.
"Mandela was the most inspiring man of his generation. His message, by example, was the power of forgiveness. He showed us that it's possible to act after great injustice with no thought of revenge. He was light, funny, enormously generous, and, quietly, the greatest example to the world that a man can be."