Sir John Chilcot, who has been appointed to investigate the Special Branch security breach at Castlereagh, is an old Belfast hand who played a key role in the Tory governments' secret contacts with the IRA.
He spent much of the 1990s as the most senior civil servant in Belfast, a post which put him at the heart not just of political affairs, but also of security and intelligence.
As permanent secretary at the Northern Ireland Office, Sir John was involved at the highest level in the most sensitive aspects of government policy, at a time when the peace process was emerging.
He worked closely with Northern Ireland secretaries and prime ministers as they grappled with the question of how to react to signs that the IRA and Sinn Fein might be ready to move into politics and talk peace.
He was also associated with the Government's approach of flatly and repeatedly denying that contacts with republicans were taking place.
Sir John began his career at the Home Office, a colleague describing him as "the best Home Office type of mandarin, really quite outstanding of his generation, an immensely subtle mind".
He has described how the then head of MI5 in Belfast, John Deverell, asked his advice after receiving a message, purporting to come from Martin McGuinness of Sinn Fein, which said: "The conflict is over but we need your advice on how to bring it to a close."
Sir John said he had been able to reassure the then Prime Minister, John Major, that the message was authentic.Reuse content