The Northern Ireland Deputy First Minister James Martin Pacelli McGuinness,(64), passes unnoticed in the lunchtime crowd at Niles restaurant in New York. Relaxed and clad in casual wear, there is little to distinguish him as a man apart.

But a man apart he certainly is. As the Sinn Fein Chief Negotiator in the peace talks that led to the Good Friday Agreement, Martin McGuinness and Sinn Fein president Gerry Adams were the prime architects of the most successful peace process in recent history.

McGuinness is on his way to Washington to attend the State of the Union and thank American politicians for their latest help with the deal reached at Christmas that saved the power-sharing government in Belfast.

President Obama had appointed former Senator Gary Hart to help out and help out he did. Sinn Fein has learned well the ability to say thanks.

The relationship between the two men who lead Sinn Fein has always been the subject of much speculation, but there is little mystery about it. Forged in the fire of IRA campaigns they had seen the worst of The Troubles and wanted it to get better. Tough, hardline but ultimately pragmatic they forged a peace that has survived innumerable efforts to break it.

In the process they galvanized Sinn Fein, making it the largest nationalist party in the North and by some polls the most popular party in the south, which has caused conniptions in the power structure there. It is an incredible achievement, one that will dominate the era when the history books are written.

The peace process was, and remains, a complete roller coaster, placing ancient enemies in power together which was never going to be easy. Now with the deal at Christmas restoring funding to the Northern Ireland Executive the process has once again been saved at the last moment.

The prospects were grim if no settlement was reached. It would have meant the certain collapse of the executive, the return of direct rule and the end of participatory government. Somehow the Rubicon was crossed.

The Sinn Fein leadership succeeded against incredible odds. So much so that my first line to McGuinness is to remark on his appearance in the Queen's speech broadcast to the British nation this Christmas.

He laughs. As the former IRA commander in Derry it must be a surreal moment when the Queen shakes your hand and puts you in her favorite home movie.

It is a measure of the journey. Politicians as diverse as Tony Blair and Bill Clinton gladly claim the Irish peace process as a huge part of their legacy, but truth be told it probably belongs in the major part to the nationalist leaders like John Hume, Albert Reynolds, Martin McGuinness and Gerry Adams who made the critical first steps.

I remark too that there is now a Sinn Fein speaker in the Northern Ireland assembly, McGuinness’s fellow Derry politician Mitchel McLaughlin. It somehow seems fitting that the man calling for order will come from a party so long accused of being disruptive and knocking off the old order.

Martin McGuinness’s journey from Bogside commander to Deputy First Minister is an amazing one, but the friendship he forged with the Reverend Ian Paisley, the unionist firebrand preacher turned politician turned deadly enemy of Sinn Fein, is perhaps the most remarkable story line of the troubles.

The two men served as the ultimate odd couple, First Minister and Deputy First Minister, and an unlikely friendship developed.

So much so that as the old man was ailing, Martin McGuinness, long time hated adversary, was one of the very few who was asked to visit with the fading Paisley.

He remembers the day well, going to the great house and sitting with Eileen, Paisley’s wife, and the preacher. Paisley had one request – that his extensive library of 50,000 books would be put on display in a special public space. Martin McGuinness promised to honor that request.

When the old man died McGuinness gave a deeply emotional and tearful tribute. He was again one of those summoned to the private family and friends moment sitting Shiva for the leading Unionist leader of the past fifty years.

It must have seemed another strange moment for the former IRA man, but McGuinness understood the humanity first and politics second of his erstwhile political opponent.

Of such moments are great political leaders made and Martin McGuinness is surely one of those.