At a time when Irish journalism appears to be benefiting greatly by ongoing disclosures revealing the respective weaknesses and slipshod practices of politicians and national institutions alike, a former national newspaper editor, himself of iconic status, has written a book honouring the forgotten achievements of one of Ireland's finest international public servants.

Douglas Gageby's account of the life and career of Sean Lester, an erstwhile journalist who joined the newly established Department of External Affairs in 1922, is far more than a history book; it is itself an act of public service. Lester served from 1934 to 1936 as the League of Nations' High Commissioner in Danzig, where he dealt with Nazism on a daily basis. Later, throughout the war he was the League's acting Secretary General and was ultimately charged with winding it down. Gageby, who had two stints as editor of The Irish Times, agrees that by writing Lester's story, he feels he is giving something to Ireland and has effectively reclaimed Lester. "But most of all I wanted to write about how a fellow from Carrickfergus, the son of a grocer, arrived at Geneva and Danzig via the Dungannon clubs." He also wants to stress the political blurring between pro and anti-Treaty sides which is central to Irish politics and is so often overlooked.

The book has been a long time in the making. "I've been thinking about writing it, oh, forever." And having finally written it, does he see himself as a writer or a journalist? "I'm a newspaper man." There is no purple prose; the language is straightforward and succinct, the content factual. He writes as he speaks. Above all, the book defers to his abiding code of journalism: "get it right". Research suits his magpie mind, and he describes the number of newspapers of the time, documents and letters he read. Lester was his father-in-law. The book is generously illustrated and he takes delight in seeing Lester's features live again in the face of his youngest son, Lester's grandson, Patrick. If currently not widely known, Lester, who died in 1959, was at one time considered a possible first president of Ireland and, as Gageby stresses, "the newspapers were full of him. When he was in Danzig he really was at the centre of international news. There were front-page headlines."

According to Gageby, Lester was "a lively but composed and resolute man", the sort of man who would - and did - treat all as equals. He refers to an anecdote he was told recently by a medical consultant who as a boy met Lester, then in his late 60s, when both were fishing in Connemara. "The man who had been that boy remarked how when they met on the banks of the river or lake, Lester spoke to him not as an elderly man to a young boy but simply as to a fellow angler." Included in the book is a colourful account of Lester meeting an immensely likeable James Joyce in Geneva. Ten days later, the writer was dead.

Long before he met Lester, Gageby had been interested in Germany, having first visited that country as a schoolboy in 1935, later as a language student, and later again as a journalist. He as the first Irish reporter to investigate the defeated Germany, sending back extensive coverage for the Irish Press. Lester for him represents the multiple ironies of Irish politics, a Northern Protestant who joined the Gaelic League where he recalled experiencing "the splendid hopes of an ancient nation's rebirth" and was also to join the Irish Republican Brotherhood. Gageby, a committed nationalist, refers to the way men such as Lester and his friend, Ernest Blythe - "he deserves a biography" - as members of a young revolutionary group known as the Dungannon Clubs, "set out to unite Protestant and Catholic Irish and to achieve the independence of Ireland". The Dungannon Clubs were founded by another friend, Bulmer Hobson, and Denis McCullough.

Gageby was born in Ranelagh in 1918, the second child of a Belfast man who had come to Dublin to work as a teenager. "He didn't mind leaving home; he used to say there was never enough food for him at his father's house." His father later became a career civil servant. Gageby's elder sister had died suddenly at the age of seven and he was raised as an only child. Although the family's return to Belfast when Gageby was almost four ("We moved in July, my birthday is in September") was attributed to his father's desire to return home, Gageby has often felt that the move was caused by his sister's death, which haunted his father. "He spoke about it a lot when I was very small and then never referred to it for years until he was visiting the Lesters before we were married, and he had long talks about it with my wife. We realised how enormously important the loss had been to him. My father was perfectly happy in Dublin."

His childhood was spent exploring Cavehill and MacArt's Fort. "I was always out and about and covered in mud, looking at some newt or other. We had hundreds of acres at our doorstep. Now it's became the Ardoyne." His interest in natural history has stayed with him, and his conversation moves quickly between a new book on the Burren, the exact whereabouts of a birch wood I mention, fishing, dogs, the number of trees he has planted at his small country house on the Boyne, and his belief that although Dublin has its mountains, "the ones around Belfast are better".

Not fully of the North, yet not entirely of the South, Gageby is not typically Church of Ireland either, but appears to have absorbed the best of all traditions and is a cosmopolitan with a countryman's instincts. His sympathy towards the North, as well as his understanding of it, have always been strong. It was he who initiated The Irish Times's coverage of the conflict by sending the late Fergus Pyle to Belfast. It marked an important development in Irish journalism, as Pyle's coverage inspired his colleagues to vie for a chance to report from there. A few years ago, when addressing the annual Parnell Summer School, Gageby referred to "the brave people of the North" and "the great city of Belfast." When a plaque commemorating the founding of the United Irishmen was unveiled in Belfast's Clifton Street cemetery in October 1995, the ceremony was performed by Gageby, who stressed "the United Irishmen were not failed revolutionaries. They were the realists. They had in common the spirit of Wolfe Tone's dictum of the name of Irishman replacing that of Protestant, Catholic and Dissenter."

One of the seminal books of his youth was Dorothy MacArdle's The Irish Republic, which was published in 1937, the year he arrived at Trinity College, Dublin.

Just as he is fascinated with history, politics and literature while avoiding the label of intellectual, his curiosity about all things protects him from being pedantic. Gageby is a blunt, direct if disconcertingly subtle, character, with a quick mind and easy humorous responses, determined and used to getting his own way. There is a jaunty contentment about him. He is compact, nice looking, seems younger than his voice and is as approachable as he is elusive, favouring peaked caps and expressions like "bloody", "damn" and an argument-clinching "go to hell". Certainly he is a man's man but one who is also liked by women.

Asked about the freewheeling In Time's Eye column, signed "Y", which has appeared daily "like mushrooms" in The Irish Times letters page since the mid-1980s and ranges from natural history to archaeology to country pursuits, local histories or the number of badgers currently killed on Irish roads, he feigns innocence and says, "you'll have to ask the editor of The Irish Times who writes that". Ah, I see. Or rather, now you see it, now you don't.

Although he preferred the outdoors, the young Gageby did well at the Belfast Royal Academy, collecting enough annual prizes to keep his father in copies of Kipling. "I always seem to have got a book by Kipling," he says with a slight trace of perhaps suspecting a plot of some kind. He liked the school. "It was an easy-going sort of place. If you wanted to do well, it was fine. But if your father owned a big shop and your future was there instead of chasing academic glory, so be it. There was no pressure." Languages appealed to him; sports didn't because of his bronchitis.

When it was time to go to university, there was no need to consider options. "My mother had always wanted me to go to Trinity. There was no question of anywhere else." Ethel Gageby came from Westmeath and was a teacher. She never lost the opinion that Dublin, and Trinity, were at the centre of Ireland. He won a sizarship and set off to Dublin where he studied French and German. There he had rooms for his entire stay. He also became interested in rowing. "We used to row out from Islandbridge to Poolbeg . . . I loved rowing; it's a great sport and if you were ever stuck for something to do, you could always paint the boathouse."

His house in Dublin includes part of a converted barn into which he and his wife decamped from the larger one behind it when their four children were grown. The lodge-like living room looks out onto a small garden which is pretty and artfully cluttered with pots and growth. Beyond the stone wall is the place where two ponies used to reside, quite a feat for Dublin 6. The books reflect his many interests and on mentioning Gunter Grass's new novel refers to the difficulty in getting German language books. "Where have all my German poetry books gone?" In common with most people who have a lot of books he suspects everyone of having removed still more. He continues to read a German daily and speaks of "that amazing, crazy people. What a culture! What a literature! I'd love to write a book about Germany." Asked for his views on journalism now, he replies warily: "I don't think people who are out of it should have a say. But I do like reading the provincial papers. I've always liked strong reporting. Working on a provincial is the best training you can get. You get a chance to cover everything." He mentions a recent agricultural show report which included the outcome of the vegetable competitions and says there was a prize for cabbages, "for rounded and pointed and I forget the third type". He does not see the speed of television news as a threat. "There'll always be a newspaper. When people see something on the television news they will want to read about it in the paper."

While not about to be drawn into a comparison between "my day and now" he does concede journalism has become more personalised. Unusually for someone with his university background, Gageby did not fall into journalism. "I was always interested. My father had spoken to me about it, he did some himself, it was where I was heading." Two things delayed this; his time in the Army and the need to complete a law degree which he had begun prior to joining up. "I wanted to know about the law, but I never practised."

He downplays his four years in the Army. Why did he join? "Because Dev asked us to - that's a good reason, isn't it?" He was an officer but likes saying he was the lowest of the low, a second. "They wanted language people." Recruited into the intelligence section, or G2, Gageby found himself translating documents into German and also spent about four months acting as the German censor for post coming into and out of the Curragh internment camp. "I didn't like that but they were careful, the letters tended to be fairly impersonal. They didn't give away much." But surely there is a contradiction in working for the army of a neutral country? His reply is brief: "Why?" and he refers me to Eunan O'Halpin's recent book, Defending Ireland - The Irish Soldier, on the question of Ireland at war. Just when it seems he doesn't want to speak about his time in the Army, his tone changes, he laughs at the memory of dodging sheep droppings in the Curragh and says, as if he has just decided, "I might write a book about being in the Army". As for the war itself, he did experience the other side. Back home in Belfast, while still a student, he remembers the night their house was bombed. "We hid under the stairs. You are always told the dining room table is the safest place. Had we been there we wouldn't have had a hope." Was he frightened? "It was bloody terrifying. I remember the lights, the sky suddenly becoming as bright as day." The house was seriously damaged. The family never returned.

There were two lives, that of Trinity student and then intelligence officer, before he was to arrive at his natural home. Back in civilian life he completed his law degree and also followed up a letter he had written to the then Irish Press editor Bill Sweetman, while still at Trinity, seeking a job in journalism. "They gave me a chance." He was hired. Having spent two years as a sub-editor, he then began his reports from Germany. Was he shocked by the changes, having been there before the war? "The place was in ruins; the people were depressed, defeated. I went around asking questions. Of course, it all depended which zone you were in. The French were particularly bitter, and it showed. The Russians were paranoid." Because of his association with The Irish Times - which he joined in 1959 as joint managing director, becoming editor from 1963 to 1974 and then returning in 1977 and staying until 1986 ("I wanted to get out before the new technology came in") - it is easy to forget, or indeed, not even to know that he reported on the Berlin Airlift. Returning from Germany, his career gathered momentum. Appointed assistant editor of the Sunday Press in 1949, he soon discovered the difficulty of adjusting to a Sunday when accustomed to the bustle of a daily. "So when I was approached to become editor in chief of the new Irish News Agency in 1952, I went."

The Evening Press was launched in 1954. By then he was the father of four children. He has been married to Dorothy Mary for 55 years. I must have looked surprised because he immediately dismissed it. "That's nothing; what's 55 years?" It is difficult to believe that when he first left The Irish Times in 1974, he was 55 "and there was this belief then in vogue that at 55 it was time to try something else." In the company of Louis Marcus he wrote and presented a six-part TV series on Ireland called Heritage. "I was looking at one of the scripts the other day; I thought it was pretty good."

While considered a generous encourager of talent, Gageby has never been known to suffer fools and, though generally regarded as fair, always had a reputation as an editor for being tough, even ruthless, and invariably an enigma. As an editor he never lost touch with Ireland or the daily business of journalism. "How could I? I wrote leaders every day for 20 years." There is little point in asking Gageby is today's Irish Times still, for better or worse, the paper he shaped. He'd never answer. But there is another question. Is it possible for a good editor to also be a gentleman? He cringes slightly. "Well, `gentleman?', I don't know about that word - but he can always be polite."

The Last Secretary-General - Sean Lester and the League of Nations by Douglas Gageby is published by Town House on September 29th, price £18.99