Who, or what, has moulded the Democratic Unionist Party into the political force it has become today? The simplistic answer might be the huge influence of one man, one leader: Ian Richard Kyle Paisley.
The real answer is much more complex and is now told as never before in precise analytical detail in a new book which was serialised in the past week in the Belfast Telegraph.
There is nothing superficial about Professor Jonathan Tonge's probe into the mind and membership of the DUP.
He traces the 40-year history of the party, from saying "No" and "Never", then "Maybe" and, eventually, "Yes" to sitting down with Sinn Fein in the Stormont Executive.
The book's researchers from Liverpool University conducted interviews with more than 100 members of the DUP, including Peter Robinson and many of his lieutenants.
Questionnaires were sent to 900 members and 52% responded. The result is a unique insight into the mind of a party which is not given to such openness.
That willingness to respond to the researchers tells us a lot about the DUP and the confidence which the party has developed to confront its critics and deal with its political opponents – most notably Sinn Fein.
So where does the DUP stand now? Firstly, it is indebted to leader Peter Robinson for the strategic purpose with which he has nurtured its political fortunes over the past four decades.
He has been around for as long as Sinn Fein president Gerry Adams and, like the latter, seems almost untouchable – no matter what crises, or controversy, he faces.
Ian Paisley was undoubtedly the public leader, but Robinson is the strategist, the architect, the back-room figure who took the DUP to where it is today.
Just as Gerry Adams and Martin McGuinness realised they could travel no further with the IRA's campaign of terror, Paisley and Robinson began to leave rejectionist unionism behind them as the DUP capitalised on the failings of the Good Friday Agreement.
Without Paisley, the change of heart could not have been sold to a party whose members would not fathom the likes of Martin McGuinness in government.
Professor Tonge's book shows that convincing the membership to share power with republicans was not easy and remains one of the leadership's greatest achievements.
Even today, the DUP harbours sceptics, but slowly the party is coming to terms with power-sharing, if only because its members fear the alternative 'Plan B' – Northern Ireland governed directly by London with Dublin input.
The Ulster Unionists kept doors open. The DUP had a reputation for slamming them shut in the face of Irish nationalism.
The Good Friday agreement hailed initially as a great success for the Ulster Unionist Party and its leader, David Trimble, has turned out to be a Godsend to the DUP.
The loose ends in the agreement, such as the failure to achieve the decommissioning of IRA weapons, the obfuscation of Sinn Fein over policing and justice and the manner in which the republicans exercised power unilaterally in the new power-sharing Executive, proved the DUP's opportunity.
The turning point was the Assembly election of 2002, when for the first time the DUP overtook the UUP at the polls – by 30 seats to 27. The defection of prominent Ulster Unionists, such as Jeffrey Donaldson and Arlene Foster, and many others led to a transfer of many thousands of votes to the DUP. The party's membership grew by 25%.
That dominance at the polls has allowed the DUP to throw back in Sinn Fein's face an obstinate negotiating attitude. The DUP's new position of majority unionist support has meant also that the British and Irish governments tread a difficult line, the DUP arguing forcibly that it has as much right, if not more, to be listened to as republicans.
The result has been a range of concessions during and after the St Andrews talks, which have restored unionist confidence in Stormont enabling the power-sharing arrangement to settle into its current state.
The modern history of rebellious, politicised Protestantism starts in 1951, when young Ian Paisley began his evangelical Free Presbyterian crusade, but perhaps the real DNA of the DUP dates back three centuries to when so many tens of thousands of disaffected Ulster-Scots Presbyterians left these shores and crossed the Atlantic.
That nomadic tribe of Protestant non-conformists took with them many of the traditional evangelical values which Professor Tonge identifies as still being at the heart of the DUP today.
It cannot be coincidence that those same values are shared in 2014 between right-wing, Tea Party conservatives in the United States and Bible-reading, church-going members of the DUP at Stormont, with outspoken views on abortion and homosexuality.
The dominance of Free and orthodox Presbyterians is still there in the DUP, but the influx of a new generation and of so many Ulster Unionists could result in a more secular future for the party.
To what extent will the DUP's gospel hall backbone be prepared to dilute faith-driven principles to attract the wider membership which is essential if the DUP is to remain in control at Stormont?
The average DUP member is male, middle-aged, married with children. He is socially conservative, right-wing, church-going, Protestant, sympathetic to, or belonging to, the Orange Order.
The number of women in the party remains low, the proportion of Free Presbyterians and Orangemen high in comparison to the general population. Though a fifth of the membership is now under 35, the average age is 51.
The past decade has seen an influx of more secular-minded members, many from the Ulster Unionists. However, devoutness to Christian teaching still lies at the heart of the DUP leadership – from Pentecostalists, such as Peter Robinson, to Baptists, Free and mainstream Presbyterians.
The membership professes a strong sense of Britishness. Even though most seem confident that the Union is safe, they believe their cultural identity is under threat.
A majority feels the Orange marches should be unrestricted, but a significant minority concedes that dialogue with nationalists is necessary in contentious areas.
The picture which the research paints is of a party which will not be pushed around. Many of its most prominent figures come from a lower social class background. In their interviews with researchers, they explain how the grassroots politics of the DUP was more to their liking.
They saw the Ulster Unionists as middle and upper-class, or drawn from the business community, much as the Presbyterian dissenters who settled in the US felt a similar sense of dissatisfaction with the Protestant establishment in Ireland in the 1700s.
Professor Tonge's analysis suggests that Free Presbyterians and members of the Orange Order hold a disproportionate influence on decision-making – even though the DUP has widened its net and adopted a more pragmatic style of politics.
The recent council and European election results suggest the DUP's support may have peaked. Unless the party can find a strategy to attract more of the huge percentage of Protestants who don't bother to vote, it runs the risk of playing second fiddle to a future First Minister from Sinn Fein.
The unionist votes are out there, but are as yet untapped.
In his interview for Professor Tonge's book, Peter Robinson expresses his frustration with his partners in power.
"Every day is a negotiating day," he says, lamenting the labyrinthine channels through which Sinn Fein operates between its Belfast and Dublin decision-takers.
That said, the DUP is sold on devolution. While the membership was slow to convince, there appears to be no turning back from sharing power with republicans.
The signs are that the speed of decision-making at Stormont is not about to change. The media and the public may complain about lack of political compromise, but the DUP is well aware that its electoral reputation is built on talking tough.
Although the old slogans of Protestant unionism – "Never, Never, Never" and "Not an Inch" – sound hollow today, no one should be fooled into thinking that the DUP is in a mood to roll over for anyone. A long haul still lies ahead.
As Professor Tonge concludes: "The DUP has become a broader party, its religious ferocity now far less overt, but it remains resolutely and unashamedly guided by points of Protestant and Christian principle."
The Faithful Tribe: voices from inside the Democratic Unionists
“I don’t think that the church should have any influence on it [DUP policy]. People’s own faith will guide them in terms of their outlook on life and, therefore, from a structural, institutional point of view, it [the score] should be a zero. But, from a personal point of view, it should be 10.”
“They can be hurtful, very, very hurtful. When I joined the council, I was going home in tears many a night — until I had to threaten that I was going to take legal action and get a solicitor to look at it.” (Describing the reaction of others after she became the first woman to be elected in her district)
Female DUP councillor
“I never got the sense being in the DUP that it is a political wing of the Free Ps ... there was a disconnect between the two even before St Andrews and those who were Free P and DUP were starting to draw the distinction between the two.”
UUP defector, now a Belfast councillor
“I certainly don't believe that the majority of people in Northern Ireland are in favour of it [gay marriage]. I certainly don't believe anywhere close to the majority of my voters are in favour of that.”
“Some people say religion and politics should never really mix. I am a total disbeliever in that aspect. If you use the Ten Commandments, you can formulate almost every law that you need.”
Paul Girvan MLA
“Inevitably, I get asked the question: ‘What about your children?’ And what is really frustrating is that you never ask that of any of my male colleagues.”
Minister Arlene Foster