Former US president Bill Clinton praised Seamus Heaney as "our finest poet of the rhythms of ordinary lives" and a "powerful voice for peace" in a tribute tonight.
The farmer's son who went on to become a world renowned Nobel laureate died in hospital in Dublin aged 74.
Mr Clinton and his wife Hillary said they were saddened to learn of the death of their "friend".
"Both his stunning work and his life were a gift to the world. His mind, heart, and his uniquely Irish gift for language made him our finest poet of the rhythms of ordinary lives and a powerful voice for peace. And he was a good and true friend," the Clintons said.
"We loved him and we will miss him. More than a brilliant artist, Seamus was, from the first day we met him, a joy to be with and a warm and caring friend - in short, a true son of Northern Ireland.
"His wonderful work, like that of his fellow Irish Nobel Prize winners Shaw, Yeats, and Beckett, will be a lasting gift for all the world."
Heaney was remembered by friends, contemporaries, admirers and politicians as a humble, warm, funny and open man as tributes flowed in from around the world.
He is survived by his wife, Marie, and children, Christopher, Michael and Catherine Ann.
A funeral mass will take place on Monday at the Church of the Sacred Heart in Donnybrook, south Dublin followed by burial in his birthplace of Bellaghy, Co Derry.
Irish Taoiseach Enda Kenny said it would take Heaney himself to describe the depth of loss Ireland would feel over his death.
"He is mourned - and deeply - wherever poetry and the world of the spirit are cherished and celebrated," he said.
The 1995 Nobel prize-winner was born in April 1939, the eldest of nine children, on a small farm called Mossbawn near Bellaghy in Co Derry, Northern Ireland, and his upbringing often played out in the poetry he wrote in later years.
The citation for the award praised Heaney "for works of lyrical beauty and ethical depth, which exalt everyday miracles and the living past".
Among the tributes, actor Adrian Dunbar led a round of applause at the bust of Heaney in the Lyric Theatre in Belfast.
It will be followed with a celebration of Heaney's life tomorrow night, which will include readings of his work and personal tributes.
Books of condolence are also to be opened at Belfast City Hall on Monday and the Guildhall in Derry city.
Heaney's publisher Faber and Faber issued a statement on behalf of the family and went on to describe the poet as a world great and an inspiration for the company.
"We cannot adequately express our profound sorrow at the loss of one of the world's greatest writers," a spokeswoman for Faber and Faber said.
"His impact on literary culture is immeasurable. As his publisher we could not have been prouder to publish his poetry over nearly 50 years. He was nothing short of an inspiration to the company, and his friendship over many years is a great loss."
Heaney was educated at St Columb's College, Derry, a Catholic boarding school, and later at Queen's University Belfast, before making his home in Dublin, with periods of teaching in Oxford University and in the US, including at Harvard.
Heaney was an honorary fellow at Trinity College Dublin and last year was bestowed with the Seamus Heaney Professorship in Irish Writing at the university, which he described as a great honour.
A year earlier he donated his manuscripts to the National Library of Ireland, a move which caused consternation in some academic circles In Belfast for overlooking his alma mater Queen's.
In 1994, a year before he was elevated to the ranks of WB Yeats and Samuel Beckett with the Nobel award, Heaney was asked while teaching in Harvard if his poetry suffered as a result of academia.
"For better or worse - I now feel for worse, earlier on I felt for better - I believed that poetry would come as a grace and would force itself through whenever it needed to come," he said.
Poet Theo Dorgan said today that poetry flowed into Heaney and through him, rather than being created.
Irish President Michael D Higgins said his contribution "to the republics of letters, conscience, and humanity was immense".
"As tributes flow in from around the world, as people recall the extraordinary occasions of the readings and the lectures, we in Ireland will once again get a sense of the depth and range of the contribution of Seamus Heaney to our contemporary world, but what those of us who have had the privilege of his friendship and presence will miss is the extraordinary depth and warmth of his personality," he said.
Mr Higgins, himself a published poet, described Heaney as warm, humourous, caring and courteous.
"A courtesy that enabled him to carry with such wry Northern Irish dignity so many well-deserved honours from all over the world," he said.
"Generations of Irish people will have been familiar with Seamus' poems. Scholars all over the world will have gained from the depth of the critical essays, and so many rights organisations will want to thank him for all the solidarity he gave to the struggles within the republic of conscience."
Heaney's world renowned poetry first came to public attention in the mid-1960s with his first major collection, Death Of A Naturalist, published in 1966.
The first poem, Digging, resonates with many today who studied it at schools on both sides of the Irish border, in much the same way as Tollund Man does in Britain for GCSE students of certain age.
As the Troubles took hold later that decade, his experiences were seen through the darkened mood of his work, such as the 1975 work North.
He addressed the violence and often discussed it in a wider historical context and wrote elegies to friends and acquaintances who were killed. But he always appeared cautious of being too closely associated with the sectarianism and division.
Heaney was never afraid to hide his Irish identity and most controversially in 1985 when he wrote An Open Letter in a spat with contemporaries Andrew Motion and Blake Morrison who included his work in The Penguin Book of Contemporary British Poetry.
Heaney objected and used the 198-line poem to remove any doubt as to his patriotism: "Be advised My passport's green/ No glass of ours was ever raised/ To toast The Queen."
The row sparked the creation of the TS Eliot Prize for a new collection of poetry for anyone from Ireland or Britain, a prize he later won for District and Circle.
Heaney's colourful objection to the British monarchy was discreetly put to one side in 2011 when he sat at the Queen's table for a banquet on her state visit to the Irish Republic in 2011, the first such trip for a ruling British monarch.
His presence was as much for his profile and the high regard he was held, as his ability to be at ease with the elite and the man on the street.
Those who knew him remarked on his willingness to accept invites, even close to his death.
He was due to deliver a speech at the Linen Hall Library in Belfast next Tuesday and make an address next month at Amnesty International's ambassador of conscience award, named after a poem he wrote for the organisation in 1985.
Among the other awards he received, a year after his Nobel win he was made a Commandeur de L'Ordre des Arts et Lettres by the French ministry of culture.
Poet Michael Longley, a friend of Heaney, said he produced "miracles right the way through his life".
Speaking to Eamonn Mallie, he said: "He was a great, great poet, a dear friend, and I'm in shock as you say."
Mr Longley said Heaney wrote some of the "best nature poems in the language".
He said: "I was very pleased that a few months ago I was able to tell him that I'd been reading his early poems, the poems he wrote as a young man, and that they struck me as miracles.
"And he joked, he says, 'well they came from Bellaghy, they'd have to have been miracles'.
"And he continued to produce miracles right the way through his life."
Belfast Poet Laureate Dr Sinead Morrissey said "poet-superstar" Heaney "seemed peculiarly destined for the kind of living success that is almost unimaginable".
Ian Martin, a writer of The Thick Of It, said he will toast Heaney and "binge-read" his work tonight.
He tweeted: "Love Seamus Heaney. Used to read his shorter poems to my daughter. 'Widgeon' she memorised. Will raise glass and binge-read Heaney tonight."
Professor James McElnay, the vice-chancellor of Queen's University Belfast where Heaney studied and taught, said: "Seamus was not only a former student, professor and honorary graduate of Queen's, but also a true friend of the university. Generous with his scholarship and his time, his warmth, humour and brilliance will be sorely missed.
"He was selfless in his contribution to Queen's. Whether giving his name to the Seamus Heaney Centre for Poetry, crafting our university's Centenary Stanza or contributing copies of his early works, Seamus asked for nothing in return.
"His contribution to the world of literature has introduced millions of people around the globe to the enjoyment of poetry and enhanced it for many more.
"As a truly inspirational citizen of Northern Ireland, he was the vanguard for a new generation of Irish poets, and at Queen's we will ensure that his work continues to inspire many for generations to come.
"At Queen's we have been truly privileged to have known Seamus as a student, staff member and Nobel Laureate and will miss him greatly."
Professor Ciaran Carson, director of the Seamus Heaney Centre for Poetry at Queen's, said: "Seamus Heaney's death will leave a void in all our lives. But his words have become part of our lives, and he endures in them. There is no poet in Ireland who has not been influenced by his example, and is in his debt; but so is everyone who has been touched by his poetry, and they are innumerable."
Motion, a former UK poet laureate, said: "Seamus was a great poet - of Ireland and the world, a brilliantly shrewd and generous writer about poetry, and a person of exceptional grace and intelligence and integrity. A wonderful man, in fact: as modest and kindly as he was gifted and principled."
Dr Patrick Prendergast, provost of Trinity College Dublin, said: "Seamus Heaney was a literary and cultural ambassador for Ireland, defining our artistic sensibility through the depth and scope of his poetry.
"He was an iconic figure in world literature, and brought to his work a uniquely Irish perspective situated in a global literary and intellectual context."
Lyric Theatre chairman Mark Carruthers said: "He was a man of enormous talents - easily the greatest Irish poet since Yeats. His loss will be deeply felt beyond the arts world."
U2 frontman Bono described Heaney as "a great, great poet" who "changed my life".
He added: "I n so many things he was a gentle genius, whose words challenged us with the grit and beauty of life as much as they gave us solace. He wrote with a brevity that strangely spilled to the brim.
"We all envied how he made that most complicated of things, the balancing of work and family, appear so simple. In Marie he found his other whole. And it is a joy to be around his kids... Michael, Chris and Catherine Ann. They have all of his humility in their sharpness."
The star revealed he carried Heaney's poetry with him, including on a recent trip to L iberia, adding: " I am bewildered to think Seamus is no longer with us. Because his words will be around forever, it seemed so would he."