Taoiseach Bertie Ahern tonight praised Ian Paisley's role in restoring devolution to Northern Ireland.
From left Bertie Ahern, Martin McGuinness, Ian Paisley and Gordon Brown before for a meeting at Stormont last year
Following Mr Paisley's decision step down as First Minister in May, Mr Ahern said: "I'm not going to say I didn't spend most of my political life taking a different point of view [to Mr Paisley], I did."
"But when it came down to making the Good Friday Agreement work and to having an inclusive executive in Northern Ireland and to have North-South bodies, he made the big moves."
The Taoiseach, however, warned Mr Paisley's departure as Democratic Unionist Party leader and First Minister would leave behind significant new hurdles.
"We've worked hard to get the stability, we've worked hard to build a relationship with Dr
"We've achieved that, it was not easy, and now the main player in a few months' time will go off the stage. "We have to now work to see if that harmonious relationship can continue. Obviously, I hope so but time will decide that."
Mr Ahern said the DUP leader had been a father figure calling the shots within the party he founded for the past 40 years.
"Now it will be a different position," he said, adding that it would be a challenge getting to know Mr Paisley's successor.
Earlier this year, Mr Ahern became the first Taoiseach to visit Mr Paisley in his heartland of Ballymena, Co Antrim, in a meeting that drew criticism from DUP hardliners.
Sinn Fein president Gerry Adams extended his best wishes to Mr Paisley and commended him for his crucial role in forging the agreement with Sinn Fein last year which restored devolution.
He said the new leader of the DUP and First Minister would have big challenges ahead of him and said it was important he came to those "intelligently and positively".
Mr Adams said: "I want to commend the positive contribution Mr Paisley has made in recent times. The agreement that he and I made last March cleared the way for the restoration of the political institutions."
"For much of his long political career Ian Paisley has been a colourful and controversial figure," Fine Gael Leader Enda Kenny said.
"However, it must be acknowledged that he is a politician of strong convictions who, once he had decided to share power with Sinn Féin, followed through fully on this commitment," he said.
Labour leader Eamon Gilmore described Mr Paisley as the most influential political figure in Northern Ireland in the last 40 years.
"In recent times, that influence has been used in a generally positive way. In earlier times in his career, it was less so," he said.
"Certainly the Dr Paisely is very different to the Dr Paisley who first led opposition to the civil rights movement and to cross-border co-operation in the 1960s. "Like many other controversial figures, history will pass final judgement on his career," Mr Gilmore said.
Minister for Foreign Affairs Dermot Ahern also paid tribute to the Northern Ireland First Minister for his remarkable political moves in recent years. "As somebody who lived all my adult life listening to Dr Paisley's diatribes against us in the Republic, there were dramatic changes and he has to be given eternal credit for the fact that he has brought back devolved government to Northern Ireland," he said.
Mr Ahern said the resignation would be one of the bumps in the road to stability in the North that was predicted last year.
"It will raise a test, I suppose, as to how solid the devolved institutions in government are and obviously the Irish Government will be doing our level best to work with whoever the successor is to the First Minister."
SDLP leader Mark Durkan said: "Ian Paisley has been a larger than life figure in politics in Ireland. His resignation is the end of an era and he has my good wishes for his retirement.
"For too much of his career he was not a force for good and while he could be politically grievous, he could be personally gracious.
"In the past few years he has at last embraced the necessity for power sharing, acknowledged the benefits of north-south co-operation and recognised the need to overcome past divisions."
The Orange Order paid tribute to the First Minister, saying: "Ian Paisley has strode across the British and Irish political scene like a giant for many years.
"No one could ignore his forthright views and while not everyone agreed with him, his personal commitment was never in doubt. "He has been particularly supportive of the Institution during the current campaign of arson attacks on Orange Halls. "We wish Dr Paisley a long and happy retirement."
PA