President Michael D Higgins led tributes to John Hume, saying we should all be "deeply grateful" for the "personal bravery and leadership" the former SDLP leader showed to bring about peace in Northern Ireland.
President Higgins said Mr Hume "transformed and remodelled" politics in Ireland and was informed by his "steadfast belief in the principles and values of genuine democracy".
"There is a greatness about his political life in what he did and what he helped to do," the President said. "I would put him in the same breath as Parnell and Daniel O'Connell."
Mr Higgins was among a number of significant Irish and international political figures to pay their respects to the giant of Irish politics.
Taoiseach Micheál Martin said Mr Hume was a "great hero and a true peace-maker".
"Throughout his long life he exhibited not just courage, but also fortitude, creativity and an utter conviction that democracy and human rights must define any modern society," the Taoiseach said.
"For over four decades, he was a passionate advocate for a generous, outward-looking and all-encompassing concept of nationalism and republicanism. For him, the purpose of politics was to bring people together, not split them apart."
Mr Martin said Mr Hume "kept hope alive" during paramilitary terrorism and sectarian strife.
Tánaiste Leo Varadkar said Mr Hume had left a "legacy of peace, progress and stability".
"His unique ability to bring people together, to embrace and respect each other's differences without being consumed by them, made him one of the most transformational figures to ever live north or south of the Border," Mr Varadkar said.
Former British prime minister Tony Blair, who was in Number 10 when the Good Friday Agreement was signed, said Mr Hume was a "political titan".
"John Hume was a political titan; a visionary who refused to believe the future had to be the same as the past," he said.
"His contribution to peace in Northern Ireland was epic and he will rightly be remembered for it. He was insistent it was possible, tireless in pursuit of it and endlessly creative in seeking ways of making it happen," he added.
Mr Blair continued: "Beyond that, he was a remarkable combination of an open mind to the world and practical politics.
"In any place, in any party, anywhere, he would have stood tall. It was good fortune that he was born on the island of Ireland."
Former US Senator George Mitchell, who chaired the talks that led to the signing of the Good Friday Agreement, described Mr Hume as a "fearless leader" and a "dear friend".
"John Hume was one of the greatest persons in Irish history, an advocate for and an architect of peace. He was rightly recognised as a fearless leader who devoted his life to the cause of peace in Northern Ireland."
U2 frontman Bono, a long-time friend of Mr Hume, described him as "the greatest servant leader of them all".
Former Taoiseach John Bruton said Mr Hume was "the pivotal figure of the 20th century in the development of thinking about Ireland's future".
"He reframed the problem from being one about who held sovereignty over land, to being one about people, and how they related to one another."
SDLP leader Colum Eastwood said Mr Hume was "20th-century Ireland's most significant...political figure".
"It is no exaggeration to say that each and every one of us now lives in the Ireland Hume imagined - an island at peace and free to decide its own destiny," Mr Eastwood said.
Sinn Féin's Mary Lou McDonald expressed her condolences to Mr Hume's family on behalf of her party.
"It is with great sadness that I have learned this morning of the passing of John Hume," she said.
There is a photograph of John Hume taken in Derry in 1969. He's standing in the middle of a street on his own with his hands raised in supplication as six policemen carrying riot shields walk towards him. His expression is calm despite the obvious tension as he implores them to stop.
"Ireland is not a romantic dream; it is not a flag; it is 4.5 million people divided into two powerful traditions. The solution will be found not on the basis of victory for either, but on the basis of agreement and a partnership between both. The real division of Ireland is not a line drawn on the map, but in the minds and hearts of its people."
When news of John Hume's death was confirmed yesterday morning, tributes began to flood in from current and former leaders of all shades of political opinion, here and from around the world.
Bill Clinton has paid a passionate tribute to John Hume. The former US President lauded him for not only being a remarkable statesman and human being, but a man whose enduring legacy of the Northern Ireland peace process has helped heal political rifts across the globe.
Appropriately enough, it all began with a credit union loan. It was 1972 and the North was enduring terrible mayhem, including the killing of 14 innocent people by British soldiers in Derry.
David Trimble, who was jointly awarded the Nobel Peace Prize with John Hume, has said the former SDLP leader's "greatest gift to Northern Irish politics" was the Good Friday Agreement. They shared the honour in 1998 in recognition of their efforts to find a peaceful solution to the Northern Ireland conflict.