The Queen is to send a private message to the wife of Martin McGuiness after he died on Tuesday
The monarch and the former IRA commander met and shook hands at a charity event in Belfast in June 2012, an event which would once have been unimaginable.
Hundreds of people gathered in Londonderry to accompany the body of Martin McGuinness on his final journey home.
Northern Ireland's former deputy first minister and an ex-IRA commander died overnight after a short illness.
An emotional Sinn Fein president Gerry Adams said his long-time friend was a passionate republican who worked passionately for reconciliation in Ireland.
"We are very, very sad that we lost him overnight," he said.
Crowds braved snow and sleet in Mr McGuinness's native Derry to accompany his coffin, draped in an Irish tricolour, from the funeral parlour to his home in the Bogside.
Another tricolour flag flew at half-mast near the Bogside's landmark Free Derry Corner.
The monarch and the former IRA commander met and shook hands at a charity event in June 2012 Martin McGuinness' life in pictures Tue, March 21, 2017
The former deputy first minister of Northern Ireland, has passed away aged 66
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Martin McGuinness and Tony Blair look on at Stormont Parliament Buildings in Belfast in 2007
Prime Minister Theresa May, Irish Taoiseach Enda Kenny, ex-US president Bill Clinton and former Democratic Unionist first ministers Peter Robinson and Arlene Foster all praised Mr McGuinness's contribution to the peace process.
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We are very, very sad that we lost him overnight
But among the tributes there were also strong words from some IRA victims not prepared to forgive the republican for his paramilitary past.
The former deputy First Minister for Northern Ireland passed away following a brief illness
John Eaglesham, whose father – a postman and part-time soldier – was shot dead by the IRA in 1978, said: "People say about what he has done for the peace process – they seem to forget that for a very, very long time he wasn't part of the solution he was part of the problem, in fact he was the main part of the problem."
Mr McGuinness, who died from a rare heart condition, completed an extraordinary political journey from an IRA leader in Derry to sharing power and a remarkable friendship with erstwhile foe, Democratic Unionist leader Dr Ian Paisley.
He also struck up a warm relationship with the Queen, whom he praised for her contribution to peace. Her Majesty is to send a personal message to Mr McGuinness's family.
The Sinn Fein stalwart is survived by his wife Bernie and four children.
Mr Clinton hailed Mr McGuinness's contribution to reconciliation.
"He believed in a shared future, and refused to live in the past, a lesson all of us who remain should learn and live by. May he rest in peace," he said.
Mrs May said Mr McGuinness was key to bringing the republican movement away from violence.
"While I can never condone the path he took in the earlier part of his life, Martin McGuinness ultimately played a defining role in leading the republican movement away from violence," she said.
Stephen Gault, whose father Samuel died in the IRA's notorious 'Poppy Day' bombing in Enniskillen in 1987, said he would remember Mr McGuinness only as a "terrorist".
"If he had been repentant my thoughts might have been slightly different," he said.
"But he took to his grave proud that he served in the IRA. There was no remorse or repentance from him, even up to his death."
Key political figures in the peace process, including former prime ministers Sir John Major and Tony Blair and ex-Irish premier Bertie Ahern, credited his efforts to bring about an end to violence.
Hundreds of people gathered in Londonderry to accompany Mr McGuinness on his final journey home
"Once he became the peacemaker he became it wholeheartedly," said Mr Blair
Sir John added: "For too many years, too many people lost their lives over the Troubles in Northern Ireland. Martin McGuinness realised that – if one wishes to secure long-term peace – negotiation must always prevail over violence. In a mixed legacy, that stands to his credit. Let that be his epitaph."
Former taoiseach Mr Ahern described the one-time IRA commander as a great leader, an extraordinary person, honest and an upfront negotiator.
"In negotiations when there is a lot at stake and it can't be a 'winner takes all' – Martin understood compromise," he said.
Mr McGuinness's last major act as a politician was to pull down the powersharing executive at Stormont when he resigned as deputy first minister in January in protest at the Democratic Unionists' handling of a green energy scandal.
The move forced DUP First Minister Arlene Foster from office.
Ten days later, showing signs of physical frailty, he announced his retirement from front line politics.
Mrs Foster, who was caught up in an IRA bomb attack as a schoolgirl and whose father survived a republican murder bid, reached out to Mr McGuinness during the recent Stormont election campaign as his health deteriorated.
"We did of course have very different backgrounds and I think it would be wrong not to acknowledge that and the fact we did have those different life experiences," she said.
"But at the same time we did have a desire to see things work here at Stormont and to make devolved government work for everybody."
Mr Robinson, who served alongside Mr McGuinness for seven years, said no other republican could have done what he did while sharing power.
"Yet while I knew his past, as he knew mine, we never doubted or gave up our shared commitment to create a new and better era in Northern Ireland politics," he said.
Mr McGuinness is survived by his wife Bernie and four children
Mr McGuinness's successor as Sinn Fein leader at Stormont, Michelle O'Neill, paid tribute.
"His leadership, grace and warm personality have transformed Irish politics for the better and his impact will be felt for many years to come," she said.
During their time in office as first and deputy first minister, Mr Paisley and Mr McGuinness earned the nickname the "Chuckle brothers".
Ian Paisley Jnr, who as a junior minister worked alongside his father and the Sinn Fein veteran during their time jointly leading the Stormont executive, said he had gone from viewing Mr McGuinness as the "godfather of the IRA" to considering him a personal friend.
"I think the Christian view in life is how a person's journey started is of course important, but it is how it finishes which is actually more important," he said.
President of Ireland Michael D Higgins led tributes from the Irish Republic, saying Mr McGuinness's death left a gap that would be hard to fill.
Mr Kenny said: "Not only did Martin come to believe that peace must prevail, he committed himself to working tirelessly to that end."