'Informer' had courage to tell the truth as he tried to make amends
Seán O'Callaghan did not expect to die from natural causes. He often told friends that the chances of him ending up with an IRA bullet in his head were at least 80pc.
This was confirmed by no less an authority than Martin McGuinness, who told the future British foreign secretary Boris Johnson in a 2000 interview: "He's got himself in an awful predicament… I mean, if he walked down the main street in Tralee, I wouldn't give tuppence for his ability to get to one end from the other."
From Sinn Féin's point of view, of course, O'Callaghan had committed the ultimate crime. He was an IRA man who gradually realised that the 'armed struggle' was morally wrong and did his best to make amends. His name rarely features on the roll call of people who brought peace to Northern Ireland - but history will show that in reality he did as much to end the violence as almost anyone.
O'Callaghan came from a rabidly republican family in Co Kerry. "My paternal grandmother told me when I was 10 that if I ever shot a policeman, 'be sure and dig him up and shoot him again… you can never trust a policeman, dead or alive'."
His father and uncle had both been interned in the Curragh and at school he was fed a diet of anti-British propaganda by the local Christian Brothers.
Not surprisingly, young Seán drifted into the republican movement and received his first prison sentence for handling explosives aged just 17.
Life for him became one long round of training camps, safe houses and bombing raids. He never denied having blood on his hands and provided a chilling description of the day he and two comrades murdered RUC chief Peter Flanagan - who was shot in a public bar and crawled into the toilet before being finished off in a hail of gunfire.
A key turning point came when O'Callaghan's commanding officer made a horrific remark about the death of a female RUC officer. "I hope she was pregnant and we have got two Prods for the price of one."
At that moment, Seán knew that the IRA campaign was not a noble battle against colonialism as he had been taught - but a dirty sectarian bloodbath largely driven by thugs and fanatics.
As a result, O'Callaghan took his own life into his hands and turned Garda informer. He embarked on a bizarre and stressful double life, rising to become head of the IRA's British campaign while secretly plotting to foil some of its most vicious operations.
Without him, this year would mark the 34rd anniversary of Princess Diana's death rather than the 20th - since in 1983 he prevented the Provos from killing both her and Prince Charles at a Duran Duran concert at London's Dominion Theatre.
Despite these successes, O'Callaghan was still wracked with guilt over his own crimes. He took the extraordinary step of handing himself in and served eight years behind bars, released in 1996 by exercise of the Queen's prerogative. Instead of quietly disappearing, he then did two things that made him a marked man for life - writing a painfully honest memoir called 'The Informer' and becoming a political adviser to the Ulster Unionist Party leader David Trimble.
As the peace process gathered pace, O'Callaghan was able to give Trimble a valuable insight into the republican mindset. On several occasions he persuaded the UUP not to pull out of talks, pointing out that this would play right into the Shinners' hands. "What [Sinn Féin] really want is unionists out of the equation," he later explained, "so they can negotiate with the British and force London to impose a settlement."
One of O'Callaghan's most shocking claims was that in 1982 Gerry Adams had asked him if the IRA should assassinate SDLP leader John Hume. "You must be bloody daft," was his reply. Mr Adams later described the allegation as "total rubbish".
'The Informer' made it quite clear that Adams had been a senior member of the IRA for decades, which prompted the Sinn Féin leader to coldly dismiss its author as "a fruit and nut case".
The reality was very different. Government sources in both Ireland and Britain often dealt with O'Callaghan and found him to be completely credible.
In person, O'Callaghan came across as an extremely nervous but kind and intelligent individual. If his background had been different, he could easily have become an excellent journalist or academic. Instead, he deserves to be remembered for what he was - a decent man who got sucked into a brutal conflict but then had the moral courage to do something that Gerry Adams and other Sinn Féin leaders have never managed.
He told us the truth.