Peter Robinson is the leader of the DUP
For more than three decades the DUP was the natural party of protest for unionists in Northern Ireland, the outsiders who challenged the establishment Official or Ulster Unionists.
But since 2007 when Ian Paisley agreed to share power at Stormont with Sinn Fein's Gerry Adams, the DUP has enjoyed being the party of government, enjoying the trappings of office and enduring the criticism which comes with it.
When Ian Paisley first became an MP in 1970 he stood as a Protestant Unionist, but his party was re-launched as the Democratic Unionists in 1971.
The party drew its support from the Protestant community and was fiercely opposed to any moves towards involving the Republic of Ireland in Northern Ireland affairs.
It campaigned against the Anglo Irish Agreement in the 1980s.
During the 1990s the DUP pulled out of the talks which led to the Good Friday Agreement in protest against the decision to invite the IRA's political wing, Sinn Fein, to enter the negotiations.
The DUP opposed the Good Friday Agreement in the referendum of 1998.
The party took departments in the Stormont Executive but refused to attend ministerial meetings in what became known as its "empty chair" policy.
The DUP benefited from growing unionist unease over power sharing and the failure of the IRA to decommission, overtaking the Ulster Unionists at the Assembly elections in 2003.
The DUP built on that achievement, confirming its dominance in the 2005 Westminster election, with the election of nine MPs.
This made it the fourth biggest party at Westminster. The DUP candidate in Upper Bann David Simpson unseated the UUP leader David Trimble who resigned shortly after the election.
In 2006 the DUP were key players in the St. Andrews' Agreement in Scotland.
Ian Paisley stepped aside as first minister in favour of his deputy Peter Robinson
In 2007, after a fresh Assembly election, the party made its historic decision to share power with Sinn Fein.
Ian Paisley served as first minister until 2008 when he stepped aside in favour of his long term deputy, East Belfast MP Peter Robinson.
Mr Robinson promised a cooler, more distant relationship with the Deputy First Minister Martin McGuinness than the "Chuckle Brothers" image fostered by Ian Paisley.
However, this did nothing to pacify the arch critic of power-sharing - former DUP MEP Jim Allister - who formed the breakaway Traditional Unionists.
Mr Allister took tens of thousands of votes from the DUP in the European elections of 2009 and, although he failed to get elected, his intervention led to Sinn Fein securing more votes than the Democratic Unionists.
The party also got stung by the scandal over expenses for MPs with five MPs having to pay money back.
In a separate issue of double jobbing for its members, Peter Robinson has agreed that double-jobbing will be phased out.
The year 2010 began with Mr Robinson facing political pressure from Sinn Fein over delays to the devolution of justice, and personal pressure due to a scandal over his wife Iris's financial dealings, which led to her resignation as Strangford MP.
The DUP leader stood aside temporarily as first minister, but resumed power after negotiating the Hillsborough agreement which provided for the early transfer of justice powers to the Stormont assembly.