At times of crisis in the peace process, Joe Cahill often arrives to offer support for the Sinn Féin leadership. Gerry Moriarty, Northern Editor, reports on a new biography of the veteran IRA figure

Joe Cahill could be classified as a guardian angel figure for Gerry Adams. Plough back through newspaper files of key public moments in the peace process when Sinn Féin and the IRA made critical but hazardous steps forward and you will find pictures of the Sinn Féin president with Cahill close by.

With his cloth cap, glasses and unassuming air, he generally said little or nothing, but didn't have to on these occasions. Cahill had - and has - clout. As a senior IRA figure for most of his 82 years, he was providing the nihil obstat for acts that republican purists would view as treachery.

In the days before the IRA ceasefire of August 31st 1994, Adams and the republican leadership felt it crucial that a respected IRA veteran such as Cahill should travel to the United States to explain to that important constituency why the cessation of violence was necessary.

As writer Brendan Anderson points out in his fine biography, Joe Cahill - A Life in the IRA, it was a shaky time, the choreography of events had to be just right. The then Taoiseach Albert Reynolds, through US ambassador Jean Kennedy Smith and President Clinton's security adviser Nancy Soderberg, was exerting pressure to obtain a US visa for Cahill, a frequently jailed and interned former chief of staff of the IRA.

Reynolds bypassed the cautious State Department and eventually tracked Clinton down to Martha's Vineyard, where he was holidaying. The then US president supported peace efforts but had some concerns about Cahill's republican CV that then went back over 50 years. In a number of phone calls, he asked Reynolds did he know what kind of a man he was seeking a visa for? "What did you expect," retorted the then taoiseach, "a parish priest?"

Cahill, as Anderson records, has read St Alphonsus's Preparation for a Sanctimonious Death while sitting in a condemned prisoners' cell, and is a practising Catholic, but his career path was never directed towards the seminary. From a young man, his basic goal in life was to see Britain out of the North and the creation of a united Ireland.

"I was born in a united Ireland and I want to die in a united Ireland," he tells Anderson.

His no-frills belief in unification might appear rather at odds with the cross-community, unionist-nationalist consensual politics of the Belfast Agreement which Sinn Fein now upholds. But - and this is to the great benefit of Adams, Martin McGuinness and other New Republicans - Cahill endorses this latest stage of the republican project.

"Stormont, for want of a better phrase, is a stepping stone. That is what is in the minds of republicans," is how he reconciles the twists and turns that republicans have taken in bringing the vast bulk of the IRA and Sinn Féin from war to relative peace.

"You hear people shouting that republicans are only interested in a united Ireland, and they are dead correct. That is republican policy. Our goal is a united Ireland, and the strategy we are using today is directed to taking us to a united Ireland by peaceful means." Cahill, as the book explains, is an interesting figure. He is gifted with an unerring strategic sense that served him well. He had high regard for the late IRA leader Cathal Goulding "as a soldier", but felt the Marxist peaceful route he was taking in the late 1960s was incompatible with the sectarian reality of Belfast at that tumultuous period.

When the Officials-Provisionals split occurred in 1969/1970 Cahill had no hesitation in siding with Seán Mac Stíofáin and Daithí Ó Conaill. He was on the first army council of the Provisional IRA, which was set up in January 1970.

Equally though, 16 years later he had little difficulty in moving with the young bloods, Adams and McGuinness, when they broke away from the politically abstentionist line of Ó Conaill and Ruairí Ó Brádaigh. In republican terms, Cahill is a man who picks and guides winners.

Cahill hopes to be at the launch by his friend and protégé, Gerry Adams, of the biography tonight in Belfast. At 82 though, he is in frail health, for which reason he cried off an arranged interview with The Irish Times.

That was a pity because it would have been useful to explore whether he now saw any strategic as well as moral value in taking Goulding's line over 30 years ago. Could all or much of that slaughter been avoided? His answer almost certainly would be no. When Anderson asked him about justification for IRA killings his response was rather predictable and along the worn no-one-has-a-monopoly-on-suffering line often used by republicans.

"In war there is no one side suffers more than the others, or less than the other," says Cahill. "In 1942 I suffered through the death of Tom Williams; it has been with me all my life. At the end of the day, this suffering will be rewarded with justice, peace, freedom. That is what keeps me going." Sixty years ago Cahill and Tom Williams were involved in a botched IRA operation in west Belfast in which a Catholic RUC constable, Patrick Murphy, was killed by the IRA unit. Cahill, Williams, and four others were sentenced to be hanged in Crumlin Road jail, but in the end only Williams - who took full responsibility for the constable's death even though bullets from two guns struck him - was executed.

Over two years ago, at a ceremony with full IRA honours, and attended by thousands of people, Williams was re-interred in the republican plot in Milltown Cemetery in west Belfast. Cahill still carries the memory of sharing a condemned cell with Williams. "Probably the hardest thing in my life was parting from him," he says.

Anderson, a lecturer in journalism in Belfast and a former security writer for the Irish News, brings the reader on a lively journey through Cahill's long republican career. It's a story of IRA activities, imprisonment, hunger strikes, face-to-face discussions with Harold Wilson, chatting to President Clinton at Stormont, successful and failed gun-running, meeting Muammar Gaddaffi in Libya, and other exploits.

Colonel Gaddaffi was happy to provide arms and explosives for the IRA but wondered why Cahill spoke English, the "language of your oppressor".

Cahill, the IRA veteran you see at Gerry Adams's shoulders on big occasions - and there could be more coming up if the IRA is to again act to push politics forwards - appears to harbour no regrets about his life and all its attendant violence.

"When I was sentenced to death in 1942 I would not have had one thought in my head about being able to work politically," he tells Anderson. "I have been part and parcel of the struggle right through, part and parcel of the present strategy, and I realise there have been sufficient changes, we have made such progress that we can now work politically.

"I believe that those who died, the Tom Williamses and Bobby Sandses of this world, if they were alive today, that would be their thinking too - that this strategy is the proper strategy. We have worked to achieve it, we have brought it about by physical force and now we are reaping the benefits of physical force and this is the way forward."

Joe Cahill - A Life in the IRA, by Brendan Anderson, published by the O'Brien Press, Dublin, €25, £16.99 sterling.