Independent Senator Michael McDowell has told the High Court that Gerry Adams falsely represented himself as a go-between in negotiations for the Good Friday Agreement when in fact he was a leading member of the IRA at the time.
The former attorney general and minister for justice was giving evidence in a defamation case that Mr Adams has taken against the BBC.
Mr Adams alleges he was defamed in a 2016 Spotlight programme and a subsequent online article, which he says falsely claimed that he sanctioned the killing of former senior Sinn Féin official Denis Donaldson.
Mr Donaldson was shot dead in 2006, months after admitting being an informer for the police and MI5 over two decades.
Mr McDowell said Mr Adams had the reputation of someone who "is a politician now who was a leading member of the IRA and who was active in the armed struggle as he calls it".
He said Mr Adams was reputed to be the chief negotiator in 1974 between the provisional movement and the British government and was reputed to have a role in Belfast as an IRA commanding officer and later an army council member.
Asked how widespread that reputation was, Mr McDowell said he had never met anyone in politics or the media who did not believe that Gerry Adams was a member of the IRA and who had not treated him on that basis.
He said in his role as attorney general and as minister for Justice he had attended many major conferences in connection with the peace process and the view of the government based on intelligence was that Mr Adams along with the late Martin McGuinness and Martin Ferris were members of the IRA army council.
He said he had never met a politician who did not believe Mr Adams was a leading member of the IRA during the armed struggle and was a dominant figure on the army council.
Asked if he as aware how the IRA treated informers, Mr McDowell said: "Of course I am aware. In general terms they executed anyone from their own ranks who was found to be a tout for the British."
Mr McDowell said the IRA continued its activities after the Good Friday Agreement in terms of weapons and fundraising through criminality right up to 2004 when he was a minister.
He said they also engaged in intelligence gathering about the then government and had kept records of the movements of Irish government ministers.
Asked if he ever recollected Mr Adams condemning IRA violence, he said whenever he was asked by journalists who eventually gave up asking Mr Adams would say he did not engage in the politics of condemnation.
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He said Sinn Féin was "always subordinate to the IRA and its army council" and the provisional movement had was better resourced than others as it had funds coming from the US.
During cross examination it was put to Mr McDowell that as a politician and media contributor and commentator he had made no secret of his hatred of Sinn Féin.
He replied: "Hatred is one word… but I abominate what they have done in the past and their dishonesty about what they did and willingness to lie right up to today about their involvement."
He agreed that his politics and Sinn Féin were on opposite ends of the political spectrum.
Asked if he agreed that Mr Adams and Sinn Féin played a central role in events leading up to the Good Friday Agreement he said he did agree but the decision by the army council to move towards a political process was in the context of the futility of its military campaign in particular its "massive infiltration" by agents.
He added: "If your asking me did Sinn Féin or Gerry Adams play a part in the negotiations that led up to the Good Friday Agreement, yes but he represented himself entirely falsely as a go-between between the IRA and the political process whereas he was in fact a leading figure in the IRA at that time."
Asked if he agreed that the Good Friday Agreement could not have happened without Mr Adams, Mr McDowell said of course it could not have happened if the IRA has kept up its bombing campaign.
Court told Gerry Adams has reputation of 'war monger'
Earlier, a victim's rights campaigner told the court that Mr Adams has the reputation of a "war monger".
Ann Travers, whose sister was shot and killed by the IRA in 1984, was giving evidence in a defamation case Mr Adams has taken against the BBC.
Ms Travers told the court Mr Adams had the reputation of supporting the work of the IRA and as a "war monger for the Troubles".
She said among victims' groups he is regarded as someone "heavily involved with the murder of innocent people and as a senior member of the IRA and Sinn Féin".
During cross examination Ms Travers said her perspective had been formed from what she witnessed on a daily basis growing up in Belfast.
She did not agree with a suggestion from Mr Adams' barrister that his reputation was overwhelmingly that of a peacemaker. Ms Travers said if she was to think about a peacemaker she would think of John Hume.
Asked if she now lived in the peace brought about by the Good Friday Agreement, Ms Travers said: "Do I live in the peace? A lot of us are still very scared."
She said anytime she criticises any Sinn Féin figure, including Mr Adams, she gets threats on social media, including death threats.
Asked if she would agree that it was now peaceful she said "of course we should all be grateful that we are not getting murdered anymore", adding "thank you to Gerry Adams for people being able to go to work now and the IRA not murdering us anymore".
She said while Mr Adams might work with victims groups he had never done anything for the groups she was involved in and most of the groups he worked with were Republican families and not families like hers who were murdered by the IRA.
Asked if her view was tainted by personal hurt and tragedy she replied: "I'm 56 years old and all I ever knew growing up was troubles, and since that all I know is that victims and survivors of both loyalism and republicanism are living with a lot of pain.
"It is a joke when he talks about being a peacemaker or denies his involvement with the IRA…he has lied consistently."
She did not agree with counsel that there would be no peace in Northern Ireland without Mr Adams.
Former rugby international Trevor Ringland told the court he believed Mr Adams had the reputation of "peace taker not a peacemaker".
Mr Ringland, who said he grew up in "a police family" in Northern Ireland and had worked with various groups in more recent years said he believed a person’s reputation could improve over the years but he did not agree that Mr Adams' reputation had improved.
During cross-examination it was put to him that his description of Mr Adams as a "peace taker" was a "soundbite".
He said the people of Northern Ireland would regard Mr Adams as a peace taker.
He said to suggest he was a peacemaker was like having someone attack you, pull you to the ground and kick you and then being told you should thank them for stopping something they should not have been doing in the first place.
He said malign causes were still damaging Northern Ireland and he believed Mr Adams "messes with peoples' minds".
It was put to Mr Ringland that while he had been a rugby player and a solicitor he was also a Unionist politician.
Mr Ringland said he had left the Ulster Unionist Party because another party member had said he would not go to a GAA match.
Declan Doyle, SC, said to him "and you then joined the all inclusive NI Conservative Party".
