But it remains a mystery how the firebrand — who for decades bellowed “No” to any compromise — suddenly said yes to sharing power with his sworn enemies in Sinn Féin.
Politicians and academics are split over how such a divisive political life has ended in unlikely harmony.
Prominent Democratic Unionist Jeffrey Donaldson, who famously ditched the Ulster Unionists to join Mr Paisley’s more hardline party, said he noted achange in his leader ahead of the 2007 deal with republicans.
“The moment it struck me that Ian had, in his own mind, made a decision, and he would go for an agreement, was after he left a meeting with the prime minister,” said the Lagan Valley MP.
He recalled how Mr Paisley told an impromptu press conference that he wanted to be remembered as a peacemaker.
“That really confirmed to me that Ian genuinely wanted to do this for the next generation,” said Mr Donaldson.
Opinion is, however, divided on why the politician known as “Dr No” finally decided to say yes.
Margaret O’Callaghan of the school of politics at Queen’s University, Belfast, studied Ian Paisley’s explosion on to the Northern Ireland scene in the mid-1960s.
She said his sectarian rhetoric had a “visceral appeal, particularly to backwoods unionism”, while he was the great “out-bidder” who portrayed other unionists as traitors.
In 1974 Mr Paisley helped smash the fledgling Sunningdale agreement that promised power-sharing between unionists and moderate nationalists.
But voters ignored his warnings a generation later, when they backed a referendum on the 1998 Good Friday peace deal.
Within 10 years, however, that low ebb was a distant memory as the DUP leader was being hailed for securing peace by going into government alongside former IRA commander Martin McGuinness.
Asked to explain the shift, Dr O’Callaghan said: “He may have become concerned about how history would see him. He had a near-death experience [in 2004].
“And also, there was no unionist rival left to ‘outbid’ him. He had been outside ‘Big House’ unionism, but in the end, he owned the mansion.”
It has been claimed that after the DUP finally replaced the Ulster Unionists as Northern Ireland’s biggest party, the British government put pressure on Mr Paisley to strike a deal with republicans. It has also been speculated that his own party colleagues wanted to secure power after decades in opposition.
But the DUP points out that its decision to enter government with Sinn Féin came after republicans had decommissioned weapons.
Seamus Mallon, a formidable figure in the nationalist SDLP and an architect of the Good Friday Agreement, said Ian Paisley’s legacy was sharply divided. He said it was unclear what led Mr Paisley belatedly to embrace power-sharing.
But he wondered if the illness that brought the unionist leader close to death in 2004 caused a shift in direction.
“His mood and his conversation and the thrust of it had changed,” said Mr Mallon.
“For many, the face of Paisley is the ugly face of threats and incitement and bigotry.
“For others — maybe a different generation — it will be that of an elderly man coming to terms with his mortality.”
Martin Mansergh, a key adviser to the Irish governments that oversaw the peace process, monitored Mr Paisley’s political journey.
“He did say to various people over the years that, effectively, he would only be interested in negotiating when he was in charge. I think that has a lot to do with it.”
In his words
Here are some more of Ian Paisley’s most notable quotes:
“People have come out of a dark tunnel and they can see there is a path out there for us. I think it has put a lot of faith and hope into people”
“We do not know how many guns, the amount of ammunition and explosives were decommissioned, nor were we told how the decommissioning was carried out. There were no photographs, no detailed inventory, and no detail on the destruction of these arms. To describe today’s statement as transparent would be the falsehood of the century”
“If anybody had told me a few years ago that I would be doing this, I would have been unbelieving”
“I believe that Northern Ireland has come to a time of peace, a time when hate will no longer rule. How good it will be to be part of a wonderful healing in our province”
“I better shake hands with this man and give you a firm grip”
“Today, we can confidently state that we are making progress to ensure that our two countries can develop and grow side by side in a spirit of generous cooperation”
“I might as well make hay while the sun shines”
Bertie Ahern: ‘Valued partner in peace and a charismatic politician’
Former taoiseach Bertie Ahern described Mr Paisley as a “big man with a big heart”.
“He was a good friend, a valued partner in peace and a charismatic politician,” said Mr Ahern.
“We both came from very different political traditions, but the more I got to know Ian Paisley, the more I respected him and the more I came to like him. In my dealings with him, I found him to be unfailingly polite and a man of his word.
“I will never forget his warmth and his sincerity that day he first shook my hand in Farmleigh on a glorious spring day in 2007.”
Mr Ahern also recalled his warm personality, booming laugh, wit, and sense of humour which he demonstrated when they first met.
“I remember at our first ever meeting, which was a breakfast summit in the Irish embassy in London, he ordered a hard-boiled egg.
“He then proceeded to tell me, with a twinkle in his eye, that this was to be sure I couldn’t poison him. It was his way of breaking down barriers.”
Mr Ahern said the clergyman showed bravery, leadership, and political acumen at a critical time for the North’s future.
“I saw how sincere he was about building peace, ending conflict, and ensuring that the next generation could live in harmony and prosperity. The remarkable culmination of all our efforts was the famous day, in May 2007, when First Minister Ian Paisley welcomed Prime Minister Blair and myself to the steps of Stormont to usher in a new era of representative government for the people of Northern Ireland.
“I know how proud Ian was to be first minister and rightly so.”
Martin Mansergh, Fianna Fáil’s former special adviser on Northern Ireland, said Mr Paisley was hugely important to the peace process by persuading the DUP to engage with it after the Good Friday Agreement and to start talking with Sinn Féin.
“Throughout his career, he was a tremendous showman. He put on a performance and the trouble is people took those performances literally and seriously and sometimes that had negative effects.
“As he gradually won control of the Unionist community in the political sense, I think he then began to reflect on what he was going to do and he decided to do something constructive with it and that was very important.
Mr Mansergh said that Mr Paisley also deserves credit for pushing the Republican movement into decommissioning and support the police in Northern Ireland.
“In the last 10 years, he did perform a big service but, of course, history will also judge his role in earlier decades as well.”
Higgins: A man of ‘deep convictions’
Ian Paisley was a man of “deep convictions”, President Michael D Higgins insisted as he led tributes to the unionist leader.
President Higgins said Paisley, who died aged 88, would be remembered for his change of attitude to power sharing.
“Irrespective of one’s political perspective, Dr Paisley was undoubtedly a man of immense influence on the contemporary history of this island.
“However, his embracing of the change necessary to achieve a discourse that might lead to peace was of immense significance, as was his commitment to building relationships in support of that peace,” said President Higgins.
Taoiseach Enda Kenny praised Paisley for embracing peace after decades of spouting division.
“I know that he treasured the peace and friendship that he had lived to see, and helped to build, between our traditions. His devotion to his faith and to the unionist people of Northern Ireland was deep and unshakeable.
“In time, history will come to a fuller judgment of his long career.
“And, while he was of course a divisive figure, his greatest legacy will be one of peace. On this day, our thoughts are with his family and our sympathies go to the many thousands of people who were devoted to him during his life,” Mr Kenny said.
Sinn Féin leader Gerry Adams expressed “shock” and sadness at the death.
“There will be plenty of time for political analysis but at this point I wish to extend my deepest sympathies to Ian’s wife Eileen and to the Paisley family at this very sad time,” Mr Adams said.
Fianna Fáil leader Micheál Martin said Paisley had embarked on an important journey.
“For over half a century, he was central to the politics of unionism and Northern Ireland. For much of his life, he was an implacable opponent of all forms of Irish nationalism. In recent years, however, he recognised the need for an accommodation and a mutual respect between all those who share this island.
“The journey he travelled, in many ways, encapsulates the triumph of the peace process and constitutional politics, and the futility of so much of what came before.
“He worked very closely with former taoiseach Bertie Ahern in bringing the Good Friday Agreement to fruition,” said Mr Martin.
Finance Minister Michael Noonan said the country owed Paisley “quite a lot”.
“He had a very long and interesting political career and where he started wasn’t where he finished. I think the country owes him quite a lot.”
McGuinness: A friend, despite our many differences
Ian Paisley’s one-time IRA foe turned partner in government has described him as a friend.
Martin McGuinness once commanded the IRA in his native Derry and faced implacable opposition from the man dubbed ‘Dr No’, whose best-known phrase was “never, never, never”.
However, Mr Paisley eventually said yes — to sharing power with Sinn Féin at Stormont in 2007. The DUP leader became first minister with Mr McGuinness as his deputy.
Mr McGuinness said: “In the brief period that we worked together in the Office of the First and Deputy First Minister I developed a close working relationship with him which developed into a friendship, which despite our many differences lasted beyond his term in office.”
Their bonhomie was evident at the many public functions they attended together, leading to them being dubbed the “chuckle brothers” by some.
Mr McGuinness added: “Over a number of decades we were political opponents and held very different views on many, many issues but the one thing we were absolutely united on was the principle that our people were better able to govern themselves than any British government.
“I want to pay tribute to and comment on the work he did in the latter days of his political life in building agreement and leading unionism into a new accommodation with republicans and nationalists.”
Sinn Féin president Gerry Adams said he was deeply saddened at Mr Paisley’s death.
“There will be plenty of time for political analysis but at this point I wish to extend my deepest sympathies to Ian’s wife Eileen and to the Paisley family at this very sad time,” he added.
His former political opponent John Hume said Ian Paisley’s death “marks the end of an era”.
The nationalist leader was at loggerheads with Mr Paisley for decades over Northern Ireland’s political future.
But Mr Hume has recalled him as a man who was capable of great charm and remembered how, despite their differences, the pair worked together on economic issues.
He said Mr Paisley had eventually embraced the politics of compromise.
“His overstated outbursts often overshadowed the understated constituency work he carried out for all the people of North Antrim whom he represented as an MP and MLA, and the tireless efforts he made on behalf of Northern Ireland as a member of the European Parliament.
“However history will record his political career as a journey — one which took him from the politics of division to a place where he accepted agreement as a solution, the need for power-sharing, and respect for diversity.
“But history will also ask if he should have reached this point sooner.”
Cameron hails courage to work with SF
British prime minister David Cameron has paid tribute to the courage of Ian Paisley in entering government with Sinn Féin.
He said: “Of course, Ian Paisley was a controversial figure for large parts of his career. Yet the contribution he made in his later years to political stability in Northern Ireland was huge.
“In particular, his decision to take his party into government with Sinn Féin in 2007 required great courage and leadership, for which everyone in these islands should be grateful.”
The prime minister’s predecessors, Tony Blair and John Major, and the North’s first minister, Peter Robinson, lauded an opponent of compromise who became a peacemaker.
Mr Blair, who presided over the restoration of devolved government in the North through the Good Friday Agreement in 1998, said: “Ian was a man of deep convictions. The convictions never changed. But his appreciation of the possibilities of peace, gradually and with much soul searching, did. He began as the militant. He ended as the peacemaker.”
John Major voiced his “great admiration and respect” for the former DUP leader, who was a fierce opponent of the Downing Street Declaration which Mr Major signed in the early stages of the peace process in 1993.
He said: “Ian Paisley was a man of public passion and huge personal charm, who cared deeply for the community he served.
“From a position where he was suspicious of every movement towards peace, he came to embrace it, and served as the first first minister of Northern Ireland. It was a remarkable journey by a remarkable man, for whom I had great admiration and respect.”
Mr Robinson said the former leader inspired the DUP. He told BBC Radio 4’s World at One: “He was a colossus in Unionism and made such a massive contribution, particularly to the process in which we are presently involved.”
Mr Cameron said he saw Mr Paisley most in the House of Commons, where his great oratory stood out.
“He had a deserved reputation as one of the most hard working and effective MPs. Ian Paisley will be remembered by many as the ‘big man’ of Northern Ireland politics. He will be greatly missed.”
Mr Robinson added: “He was more than a significant figure. Ian was a founder and inspiration behind the existence of the party.
“He led it through difficult times where the Unionist community in Northern Ireland was under attack from terrorism and felt that their constitutional position was imperilled, right through from those dark days to the relative peace and security that we have at the present time.
“He was instrumentally involved and a key figure in terms of entering into the agreements that made it all possible.”
In his words
Here are some more of Ian Paisley’s most notable quotes:
“They breed like rabbits and multiply like vermin”
“Catholic homes caught fire because they were loaded with petrol bombs; Catholic churches were attacked and burned because they were arsenals and priests handed out sub-machine guns to parishioners”
“Save Ulster from sodomy!”
“Never, never, never, never...”
“I am not going to sit down with bloodthirsty monsters who have been killing and terrifying my people”
“The scarlet woman of Rome”
“I don’t like the president of the Irish Republic because she is dishonest”
“Mr Adams would have to repent from his evil ways. I am here tonight by the grace of God, a sinner saved by grace”
“Talk about dancing at Christmas on the graves of Ulster dead, and to be given the facility so to dance by the British prime minister... Here we saw the godfathers of those who planned the bombing of Downing Street, standing outside there and piously pretending they were engaged in a search for peace”
“I denounce you, antichrist! I refuse you as Christ’s enemy and antichrist with all your false doctrine”
“This Romish man of sin is now in hell!”
“The IRA’s bishop from Crossmaglen”
“Line dancing is as sinful as any other type of dancing, with its sexual gestures and touching. It is an incitement to lust.”
“No surrender. We will never bend the knee”
“Protect us from the shackles of priestcraft”
“The breath of Satan is upon us”
“Let me smell your breath first, son”
“The devil’s buttermilk”
“This is the spark which kindles a fire there could be no putting out”
“Because it would be hard for you to poison them”
“No, I wouldn’t”
“I would never repudiate the fact that I am an Irishman”
“I will never sit down with Gerry Adams ... he’d sit with anyone. He’d sit down with the devil. In fact, Adams does sit down with the devil”
“We are not going into government with Sinn Féin”