Northern Ireland had never seen anything quite like George Mitchell before. This is a society marked by sectarian division where some political parties are not even on speaking terms and where, in Matthew Arnold's phrase, "ignorant armies clash by night".
Political systems that lack even basic civility have little hope of making social and economic progress. George Mitchell radiates civility and that intangible quality may prove to have been his greatest single contribution to the talks process.
He had not been known for his intense and sustained interest in the Irish Question and his name did not feature in the litany that began with Ted Kennedy and included the likes of Peter King, Chris Dodd, Benjamin Gilman and Daniel Patrick Moynihan.
Mitchell became seriously involved when he was appointed President Clinton's economic adviser on Northern Ireland. I first encountered him at an economic seminar organised for Clinton's benefit in east Belfast during the 1995 visit. I was struck by the obviously genuine affection with which he spoke of the ordinary people of Northern Ireland from both traditions.
The senator's involvement deepened when he agreed to head the three-member international body on the decommissioning of paramilitary weapons. This issue had become a major stumbling-block to progress. Speaking in the US capital, Sir Patrick Mayhew had made decomissioning of IRA guns and bombs a precondition of Sinn Fein's entry to talks: known in peace process shorthand as "Washington Three".
Since the IRA kept repeating it would not hand over a single bomb or bullet and since decommissioning would have to be voluntary, it looked as if the British government had impaled itself on a hook from which there was no escape.
Enter Mitchell and his co-chairmen, Harri Holkeri and Gen John de Chastelain. They met everyone and listened to their views. As a former judge, Mitchell knew how to make it clear to all that he was weighing the evidence soberly and carefully. Previous documents in the peace process had been noted for their obscure and ambiguous language: Mitchell's report when it came was a model of clarity, written in simple, pellucid language and providing what many saw as a dignified compromise solution to the problem.
After that it was almost inevitable he would be nominated to chair the multi-party talks. There was bitter opposition from hardline unionists who saw him as Clinton's man and an agent of the Irish-American lobby. But even some of his critics were impressed by his calm and composure.
After a rocky passage, his chairmanship went through. But that was only the beginning of his problems. Month after tedious month he sat in Stormont's Castle Buildings as the talks stumbled along.
Decommissioning was moved to the sidelines, the IRA called another ceasefire and the way was clear for Sinn Fein to enter the talks at last. But when that prospect loomed, the DUP and UK Unionists walked out.
Despite these ups and downs, Mitchell never showed any public impatience. He has addressed the media on good days and bad days in the process but always with the same self-possession, lucidity and good humour. Unlike other politicians who sit at the table in Stormont's Portakabin Maximus, Mitchell speaks from a lectern: it's more formal and seems to have a calming effect even on reporters with only minutes left to deadline. George Mitchell's transatlantic peregrinations to sort out an ancient quarrel may now be drawing to a close but, whatever the fate of the agreement he brokered, his legacy of quiet dignity will endure.