Progressive Unionist Party leader David Ervine has died in a Belfast hospital at the age of 53.
PUP leader David Ervine
Mr Ervine - who suffered a heart attack, a stroke and brain haemorrhage - had been on a life support machine for 24 hours.
His wife, Jeanette, and two sons were by his bedside when he died at the Royal Victoria Hospital in Belfast.
Mr Ervine, who was imprisoned in the 1970s for possessing explosives as a member of the Ulster Volunteer Force, was regarded as one of the most forward-thinking unionists for supporting the Belfast Agreement and his pivotal role in brokering the loyalist ceasefires of 1994.
He was the centre of a political storm in March last year when his UVF-linked party joined the Ulster Unionist Party's Assembly group, to cries of condemnation that the UVF had not left violence behind.
Taoiseach Bertie Ahern said he was "greatly saddened" of the death of Mr Ervine, describing him as "courageous and articulate." Mr Ahern said his presence would be missed as final steps are being taken to bring about the return of power-sharing to the north.
British Prime Minister Tony Blair said in a statement Ervine was a man who played a major part in trying to bring peace to the North over the last decade, whatever his past.
Known to enjoy smoking a pipe, eating Irish stew and supping a pint of Guinness, Mr Ervine has subverted the familiar image of the bowler-hatted, white-gloved unionist.
In 1997, he called for an end to the "cacophony of bombs, bullets and beatings" in the North. In 2001, then Northern Ireland secretary John Reid described him as "possibly one of the most eloquent politicians in Northern Ireland".
Mr Ervine is the youngest of five children of non-practising Presbyterian parents. His father, Walter, was a member of the old Northern Ireland Labour Party.
Mr Ervine rejected the Orange Order and also kept away from paramilitary organisations until Bloody Friday in July 1972, when the IRA detonated more than 21 bombs across Belfast in under an hour, killing nine people and injuring more than 100.
He became a secret UVF volunteer - not even his wife knew - until he was arrested in 1974 and sentenced to 11 years for transporting a bomb.
Imprisonment in Long Kesh may have done much to develop his thinking. Under the guidance of loyalist veteran Gusty Spence, he argued politics, sat O-levels and studied humanities, arts and social sciences. He was released in 1980.
He joined the fringe left-wing Progressive Unionist Party in 1985. In 1998 he was elected Assembly member for East Belfast and was re-elected in 2003 though the party lost its other seat in north Belfast. He succeeded Hugh Smyth as leader.
Last May, amid the problems over the restoration of devolution and controversy over his UUP alliance, he said: "The next phase of the process is parliamentary democracy. Let's get on with parliamentary democracy."