Figures from across the political spectrum have paid tribute to Brendan Duddy, who died on Friday, aged 80.
Born on 10 June 1936, the Londonderry businessman become known as "Northern Ireland's secret peacemaker".
For more than 20 years, he acted as secret back-channel between the British government and the IRA leadership.
He was at the centre of a chain of events that ultimately led to the historic IRA ceasefire of 1994 and the Good Friday peace agreement.Image copyright Twitter
The DUP leader Arlene Foster said on social media, "(It) was lovely to meet Brendan again in recent weeks.
"Deepest sympathy to the Duddy family. They mourn a man who worked hard for a shared NI."
Sinn Féin President Gerry Adams tweeted "I am very sorry to hear of death of Brendan Duddy. A decent man who did his best."
He added, "Brendan was a tireless advocate for peace over four decades.
"There was always a constant in his determination and commitment to finding agreement, achieving progress, and ending conflict."Image copyright Twitter
The leader of the Catholic Church in Ireland, Archbishop Eamon Martin praised Mr Duddy's work throughout the Troubles, tweeting, "In a world of violence, conflict and threats of war, we need more people like Brendan Duddy. Rest in Peace".Image copyright Twitter
Danny Kennedy, from the Ulster Unionist Party, tweeted: "Sorry to learn of the death of Brendan Duddy. I served with him on the NIPB (Northen Ireland Policing Board) for a brief period. He was a fine and honourable man."
The SDLP MP Mark Durkan tweeted: "Brendan Duddy RIP - Ear for thinking, tongue for explanation, eye for nuance, head for ideas, heart of peace. "Tutored" me during Hume-Adams."
The Irish Foreign Affairs and Trade Minister Charlie Flanagan said he was "saddened" by Mr Duddy's death, adding that he was a "quiet hero".Image copyright Twitter
BBC reporter Peter Taylor, who made a documentary about Mr Duddy, said he was the "unsung hero of the Troubles".
The veteran journalist, who has reported extensively on the Troubles, told the BBC: "I don't think the part he played has ever been fully recognised and his place in history will be quite rightly secured.
"The fact we have a relative peace in Northern Ireland would not have happened without the remarkable efforts Brendan made.
"I'm sure that took its toll on him. He was a very fit, athletic, agile man. I think it took its toll in the long term and he did it at great risk to himself and his family."Image caption
During the civil rights demonstrations of the late 1960s, Mr Duddy ran a fish and chip shop whose beef burgers were delivered by young van driver called Martin McGuinness, the future IRA leader and deputy first minister, who died in March this year.
While Mr Duddy's public face was the family business, he got a taste of the role as go-between just before Bloody Sunday in 1972, when he was asked by the police to persuade IRA members to remove their weapons from the Bogside.
After Bloody Sunday, Mr Duddy met an MI6 officer called Michael Oatley and became the secret channel between the British government and the IRA, that would last until the 1990s.
Codenamed "Soon", he was the key link between then Prime Minister Margaret Thatcher and the IRA during the 1981 hunger strikes.
Famous in ColumbiaImage caption
In the early 1990s, he hosted talks at his own home in Derry between Mr Oatley and the intelligence services, and Mr McGuinness and the republican leadership.
According to Mr McGuinness, Mr Duddy's successful role in the peace process was so renowned it even reached Colombia.
In 2014, the Sinn Féin politician said that when he met President Juan Manuel Santos, the Colombian leader told him that when his government opened a back channel with the rebel group Farc, the negotiator was codenamed "Brendan".
While playing the role of peacemaker, Mr Duddy also grew his business empire - the family firm, Duddy Group, has interests in property, bars, restaurants and hotels, including Derry's City Hotel and the Ramada Hotel in Portrush.