Sinn Fein's Martin McGuinness has travelled a long political road since his role in the IRA, but unionist hard-liners remain angry that today's deal will see him share political responsibility for law and order in Northern Ireland.
Republicans claim that his highly influential term as Deputy First Minister has helped him deliver what was once thought to be politically impossible.
Over the last three years he has struck up an unlikely partnership with Ian Paisley, branded dissident republicans "traitors", and withstood taunts that the DUP was blocking Sinn Fein policies in the Assembly, while he also backed the power-sharing government when others in his party were tempted to pull the plug.
His harshest critics will never forgive his self-confessed role in the IRA, while others paint him as a wily political operator who has engineered a crisis to secure the devolution of policing powers away from Westminster and on to the island of Ireland.
But colleagues and close observers claim that, by showing a willingness to work with unionists, and by facing down death threats from disaffected republicans, Mr McGuinness has been able to "bank" political capital and is now profiting.
A Sinn Fein source said: "There were times over recent years where there was tension between people in the party who wanted to put it up to the unionists, who thought they were just creating space to get at us, to insult us in the Assembly.
"But it was often Martin who said, no, it was right to wait and that we should prove the institutions can work."
As recently as December, the DUP seemed reluctant to agree a deal on devolving policing and justice powers with republicans, which would hand the Stormont administration responsibility for policing and for the courts system.
It repeatedly rejected claims that it was bound to do so by the terms of the St Andrews agreement of 2006 which had led the two parties into government.
And as the controversy grew, it seemed certain that Sinn Fein was set to pull the institutions down in protest.
But by last month a scandal was sparked by the revelation that Democratic Unionist MP Iris Robinson, wife of party leader Peter Robinson, had secured £50,000 from two property developers to set up a business for her teenage lover.
Suddenly there was a perception that the DUP feared it would suffer severely in a snap election which would follow a collapse of the Assembly.
Critics claim, therefore, that good fortune has helped Sinn Fein and Mr McGuinness secure today's political gains. Others claim the Derry republican has "made his own luck".
When the seemingly impossible was achieved in 2007 and the DUP and Sinn Fein entered government together, the then First Minister Mr Paisley took to calling his political partner "my deputy".
But while Mr McGuinness knew the role of Deputy First Minister was equal in all but name, he gritted his teeth.
Thereafter the men struck up a remarkable rapport, regularly sharing jokes in public, and with the younger man displaying a readiness to show some respect for his older colleague.
One republican said: "I remember when the two of them were in the US and Paisley lost his train of thought during a speech. Martin stepped in and glossed over it to help Ian."
It has also emerged the former enemies even prayed together around the death of Mr McGuinness's mother.
In mid-2008 the so-called "Chuckle Brothers" were split up when Mr Paisley stepped down as DUP leader and a new era began with the arrival of Mr Robinson.
The DUP wanted to show a tougher face, and the East Belfast MP was just the man for the job.
But it was the Deputy First Minister who carved out one of the most notable political moments of the period when dissident republicans murdered two soldiers and a policeman last March.
Standing next to Mr Robinson and the then chief constable, Mr McGuinness branded dissidents traitors to the people of Ireland. Given his own past, it was a dramatic intervention.
By late last year, there was a growing feeling in Sinn Fein that their man's defence of the peace process was not being matched by the DUP, which, it claimed, was stalling the devolution of policing powers.
Mr McGuinness, who gets up at 5.30am each day to travel from his home in Derry to the Assembly in Belfast, often not returning until midnight, was getting increasingly impatient with the political impasse.
A source with long experience of the senior republican said: "I know that people were saying to McGuinness 'Why are you letting yourself be treated like this?'.
"I know he can be patient, but recently I think he felt he may have to walk. And in those circumstances he would cut you off as quick as look at you. The unionists realised that."
Under today's deal a new Justice Minister will be drawn from outside DUP and Sinn Fein ranks, but both parties will continue to lead the administration that will now boast its new law and order powers.
Last year Mr McGuinness was among senior Sinn Fein colleagues who addressed supporters in Co Tyrone. He told the audience it was now the task of republicans to "make friends with unionists".
This is dismissed by opponents, who note he openly acknowledges his former membership of the IRA. But a recent opinion poll of Catholics and Protestants voted the Deputy First Minister the Assembly's most impressive politician.
It marked a further milestone in his unpredictable political journey and added to the impression that when this period of the peace process is reviewed, Mr McGuinness may emerge as the chief political beneficiary.