Peter Robinson's decision to stand down as DUP leader and First Minister is a big moment in Northern Ireland politics.
It means unionism is losing its chief strategist, realist and pragmatist, the politician who helped persuade both Ian Paisley and the bulk of the unionist community to share power with the Sinn Féin arch enemy.
He has shown a surprising wisdom in announcing that he is shortly to step down. After his recent heart scare - surely exacerbated by the enormous work load he subsequently had to endure in trying to achieve this week’s Stormont agreement - the hard stresses of political life have been etched on his face.
Enoch Powell said most political careers end in failure. Robinson has confounded that maxim to a considerable degree: he is beginning to pack his bags at a time when the two dominant players in Northern politics, his DUP, and Sinn Féin, have formed a concordat that, with the right will, should stabilise Stormont for the period ahead.
Nationalism will probably never love him but history will be kinder: like Ian Paisley, the man he walked with for decades but from he became estranged, he finally learned the lesson of Sunningdale for slow learners.
He even may still have the power to put his seal of approval on his predicted chosen successors: North Belfast MP Nigel Dodds as leader and Arlene Foster as First Minister, a quasi duumvirate that may be able to keep united the fundamentalist and, relatively speaking, more liberal wings of the party.
There are other internal strains in the party. For example it is well-known that the Paisleys and the Robinsons don’t get on - the Paisleys believing Robinson was guilty of an act of “betrayal” in prompting the ‘Doc’ to quit as First Minister and DUP leader in 2008.
The Robinson camp response was it was no act of treachery, that at 82 it was time for Paisley to go, just as at the much younger age of 66 Robinson has figured it’s time for him to go. And when he is ahead.
So far - and it is early days - Ian Paisley junior, the DUP politician viewed with most cause to spoil the valedictory and succession party of the coming weeks, has not given any indication that he would want to upset the carefully planned farewell preparations.
One senior DUP figure thought that while Ian junior might view Robinson as a “control freak” he probably wouldn’t be “so churlish” as to put a dampener on the DUP leader’s leaving.
Robinson indeed is a man who likes to have his ducks in neat linear formation. His announcement isn’t a surprise and one can assume he has been doing preparatory work to keep both strands of the party satisfied.
One can expect that if and when Nigel Dodds is installed as leader that in divvying out the Ministries and the other baubles that both strands of the party will be kept happy.
Like Sinn Féin the DUP always has been a centrally controlled, strictly run organisation. Remember that in its 44-year history it only has had two leaders, Ian Paisley for 37 years, Robinson for seven.
And for much of those 44 years they were a double-act: Paisley providing the charismatic, demagogic drive and attraction; Robinson his firebrand deputy there at the barricades and on the hillside when required, but later steering Paisley towards an historic accommodation with republicanism and nationalism in March of 2007.
That was when both saw the time was right - when the DUP was the unassailable top dog of unionism.
And like Gerry Adams and Martin McGuinness they were some twosome. Robinson became involved in full-time politics in 1971 after the IRA murder of a close friend, Harry Beggs. Quickly Paisley saw how formidable, ambitious and determined was his young lieutenant.
They soldiered together in battles such as the unionist-loyalist overthrow of the 1974 power-sharing Sunningdale government, the formation of the sinister unionist-loyalist Third Force in 1981, in protesting against the 1985 Anglo-Irish Agreement, in helping establish Ulster Resistance in 1986 and creating some distance from that organisation when it started gun-running for loyalist paramilitaries, and in railing against the 1998 Belfast Agreement.
Paisley was cute enough to be out of the country when Robinson was arrested and subsequently fined and dubbed ‘Peter the Punt’ for leading a loyalist mob in invading Clontibret in 1986, another act of defiance against the Anglo-Irish Agreement of 30 years ago.
But there was always that pragmatic political dimension. With the late UUP MP Harold McCusker and UUP general secretary Frank Millar, a former London editor of The Irish Times, he was involved in the unionist Task Force which in 1987 came up with proposals that didn't rule out sharing-power with the SDLP.
Paisley disapproved and it led to Robinson temporarily resigning as deputy leader although he was back in the fold within months - Paisley recognising that he could not function successfully without him.
This desire for political power was also demonstrated in 1999 when notwithstanding the DUP’s opposition to the Belfast Agreement Robinson persuaded Paisley that he (Robinson) and his now favoured successor Nigel Dodds should enter the power-sharing Northern Executive, if in a slightly detached fashion.
Personally Robinson had to cope with the trauma of his wife having an affair with 19-year-old Kirk McCambley and the consequent controversy that almost caused him to lose his leadership early in 2010.
Yet he showed courage and he prevailed although later in 2010 he lost his East Belfast Westminster seat, an experience that perhaps taught him a lesson about political mortality.
Despite these travails no one can gainsay that Paisley with Robinson and then Robinson on his own led the DUP to become the undisputed dominant unionist party, overthrowing the UUP.
But whatever about his health Robinson has been politically weakened in recent months. For once he was outmanoeuvred by the Ulster Unionists when leader Mike Nesbitt withdrew his Minister Danny Kennedy from the Northern Executive after the police assessment that IRA members along with others were involved in the murder of Belfast republican Kevin McGuigan.
This in turn led to Robinson standing aside from his post as First Minister and pulling all his Ministers out of the Executive apart from Arlene Foster who remained as acting First Minister and Minister of Finance.
The DUP Ministers who resigned reappointed themselves for a couple of hours more or less on a weekly basis in a much derided “in out” basis.
This was to avoid the Ministries being allocated to other parties. It was lampooned as the Robinson Northern Executive “hokey cokey”.
And when the British government appointed panel found that yes that police assessment was correct, that the IRA still existed and its army council was still operating, Robinson turned the report on its head by somehow finding this was sufficient for the DUP to remain in the talks that led to Tuesday’s agreement.
This caused unease in the party, an anxiety that were Robinson to hang in as leader the party would be damaged and face a UUP resurgence in the coming May Assembly elections.
The Nama controversy and the fact that he had to go on record to deny that he benefited or was to benefit from the £1.24 billion property deal just piled on more pressure at a time of huge strain. There has been no evidence and no smoking gun that implicates Robinson but just having to make those statements of innocence must be injurious.
As was noted time and time again Robinson politically was doing what David Trimble had to do in the past, perform political somersaults to keep Stormont working.
It must have been mortifying for Robinson but still he did it. The reward was the latest Stormont deal and the means by which Robinson could begin his exit with his political legacy fairly intact, even if his political dignity was upset.
There will be plenty who will be grudging but as Othello and Charlie Haughey said he "did the state some service, and they know't". The stress lines might now start to recede a little.