David Ervine, leader of the loyalist Progressive Unionist Party in Northern Ireland, died in hospital today.
Mr Ervine, who suffered a heart attack, a stroke and brain haemorrhage, was 53 and had been on a life support machine for 24 hours.
The PUP chief was a central figure in securing the 1994 loyalist paramilitary ceasefire.
His wife Jeanette and two sons were by his bedside when he died at the Royal Victoria Hospital in Belfast.
Ken Wilkinson, one of his closest political associates, said he was devastated by his party leader's death.
Mr Wilkinson said: "I don't think Northern Ireland realises the sacrifices this man made.
"He was a good friend to me, but more than that, it's a sad a loss to the people of Northern Ireland.
"When they look back in history, they will see what David Ervine contributed."
Mr Ervine, a member of the Stormont Assembly for East Belfast, was taken to hospital after suffering a heart attack at his home yesterday.
As his health worsened, he was transferred from the Ulster Hospital on the outskirts of the city to the Royal Victoria.
Mr Ervine led the PUP, which is aligned to the loyalist paramilitary Ulster Volunteer Force, since 2002.
He became recognised as one of working class loyalism's most articulate voices after coming to public attention following the ceasefire called in response to the Provisional IRA's first halt to its violent campaign.
Like some Sinn Fein representatives elected to the Stormont Parliament after the 1998 Good Friday Agreement, Mr Ervine moved into politics after being imprisoned for paramilitary crimes.
He served time in the Maze Prison near Lisburn, Co Antrim, after being arrested driving a car bomb in 1974.
Mr Ervine said he was sucked into paramilitarism after the IRA killed nine people on Bloody Friday in July 1972.
During his time in prison, he studied to Open University degree level and following his release became active in the UVF's political wing.
A passionate politician, he supported the Good Friday peace deal, having participated in the talks which led to them chaired by Senator George Mitchell.
In 1998 he captured an Assembly seat in East Belfast along with his party colleague Billy Hutchinson, who won a seat in the north of the city.
Five years later, while Mr Ervine retained his seat, Mr Hutchinson lost his.
The PUP leader hit the headlines last year after the Ulster Unionists admitted him into their Assembly Group, even though he was not a party member.
Ulster Unionist leader Sir Reg Empey justified the move despite internal criticism on the grounds that it would encourage the UVF to move away from violence for good and also guarantee a unionist majority on any future power sharing government.
Assembly Speaker Eileen Bell later ruled that the move to accept Mr Ervine was invalid.
Mr Ervine's son Mark told PA: "David passed away quietly, peacefully and with dignity at lunchtime.
"The family would like to thank staff at the Ulster and Royal Victoria Hospitals for all they did for David and the family.
"We would ask the media to respect our wish for privacy at this sad time."
Prime Minister Tony Blair said in a statement that he was "very sorry" to learn of Mr Ervine's death.
"David was a man who, whatever his past, played a major part in this last 10 years in trying to bring peace to Ulster," he said.
"His incisive wit and clear, if often controversial, analysis of Northern Ireland politics marked him out.
"Brought up in sectarian politics, he ended up being a persistent and intelligent persuader for cross community partnership and he will be sorely missed."Reuse content