With the success of Shadowlands the world now knows about C S Lewis, the Oxford English don, theologian, philosopher and writer of both science-fiction and inspired children's books, who died in 1963. The film centres on his late and ecstatic marriage in 1956 to an American woman called Joy Gresham, who died of cancer less than three years later. Few know that, at the very end of Lewis's life, when he himself was very ill, he met another American, dubbed by Lewis's friends 'the great Lewisolator'. His name was Walter Hooper.

Hooper first visited Oxford in 1963, the year of C S Lewis's death. Tony Nuttall, now an English professor at New College, Oxford, remembers: 'I was in the administrative office of the summer school when a little chap walked in and asked for Louisiana. I said: 'You cross the Atlantic and turn left.' He said: 'No, no, I am looking for works pertaining to C S Lewis.'

'Well, after this, Hooper hung around outside C S Lewis's house, where he was very ill. Somehow Hooper got in, and after a few days a little council of war was held in the nearby pub. The Merton don, Hugo Dyson, a great friend of Lewis's, was sent to investigate and emerged from the house saying, 'It's all OK, Jack likes him'.'

Today Walter Hooper, now aged 62, still makes his home in Oxford: 'That's what one cup of tea with Lewis turned into]' He goes on: 'Lewis didn't need me to nurse him; he had a male nurse already. He had been ill for some years with an infected kidney, but they couldn't operate because his heart was too weak. I found him absolutely unconcerned about his health. But one of the great burdens of his day was the daily post - he got so much and always thought he had to respond by return. He dictated the most wonderful letters, so he really did need my help.

'As we got on very well, he asked me to stay on as his private secretary, so I moved in. In August I had to go back to America. While I was away we corresponded about the future and were making plans, but Lewis died before I could return, on 22 November 1963, about an hour after President Kennedy was shot.'

Who was this young American who arrived so opportunely out of the blue? Walter Hooper was born and raised in a tiny town in north Carolina called Reidsville, in the heart of tobacco-growing country. His father was a central-heating engineer; his mother, aged 87, is a housewife.

'I went into the Army in January 1954 and had picked up a very popular book called Letters to Young Churches by J B Phillips, which had an introduction by C S Lewis, and I was struck by the fact that this man had a confidence in God that I'd never seen before he really believed. I managed to get a copy of Miracles and read it while I was in basic training. I had it inside my shirt as I threw grenades. I could only read for five minutes an hour, but it opened up a new world to me. I wrote to thank him, and had a letter back, and thus began a copious correspondence. Meanwhile I read every single work of his.

'I hero-worshipped him, and still do. I can't think of a better way of spending my life than by making his contribution better known.'

In January 1964, Hooper came back to England for good: not that he realised it at the time. C S Lewis's elder brother, Warren, asked him to undertake the editing of the Lewis papers and Hooper agreed. C S Lewis has been Hooper's life's work ever since.

Hooper was ordained in 1965 as an Anglican clergyman (converting to Roman Catholicism in 1988), but he always earned a pittance. In 1971 C S Lewis's stepsons offered to put him on a salary, and for the first time he was not living in penury. Lewis's relations and friends were only too glad that someone was prepared to undertake the enormous task of finding and publishing all that remained of his work.

What sort of man can inspire such hero-worship? Clive Staples Lewis was born in Ireland in 1898, and announced at the age of four that he wanted to be called Jack. His father was a Belfast solicitor; his beloved mother, Flora, died when he was a small boy. It was the first great grief of his life. His father became unpredictable, wild of temper, and the two sons - Jack and Warren, three years older - were sent off to boarding school, which Jack loathed. In 1917 Jack went up to University College, Oxford, but in November that year he was posted to France, a second lieutenant in the Somerset Light Infantry, and sent up to the front line.

Lewis made many good friends in the Army, among them a man called Owen Barfield. Barfield, now 95, says: 'His prime quality, apart from his blazing intellect, was his humour - it was fun talking to him - and his genuine interest in what was going on around him, as long as it wasn't politics. I would say he was the best friend I had in my life.'

Barfield tells of another friend from the First World War days, Paddy Moore: 'They made a pact that if one were killed, the other would look after his surviving parent. When Paddy was killed, Lewis fulfilled his side of the pact: he found Mrs Moore in Oxford and looked after her for the rest of her life. He was always ready to do the dirty work around the house, quite contrary to his natural inclinations. She's been depicted as a kind of tyrant, but that wasn't the impression my wife and I got at all. We were quite fond of her.

'People have argued that Jack had a relationship with her. It's certainly possible, but unlikely to have been long-enduring; she was quite a lot older than him, and not, I should have thought, physically attractive.'

Humphrey Carpenter, who has written about C S Lewis, puts it more strongly: 'Lewis used his conversion to Christianity (in 1929) to jettison Janie Moore, with whom however he had until then almost certainly been having an affair. But thereafter he formed no other liaison; he looked after her till the day she died. Joy Gresham came into his life shortly after Mrs Moore's death, and she was a very similar character: tough, forthright, outspoken.'

The writer John Wain, who was taught by C S Lewis in the mid-Forties, says: 'Because of Mrs Moore, he spent his early years in a great deal of poverty. He dared not tell his father about his entanglement with her, and the allowance his father gave him wasn't nearly enough to support them both. It was then that he formed frugal habits. Although he loved books, he never bought one if he could get it from the library. He had bachelor's habits, fag-ash all over himself - he wasn't too poor to smoke or drink beer, though in those days it was very cheap.'

In due course the huge popular success of his books - in particular The Screwtape Letters, first published in 1942, and Surprised by Joy, in 1955, made Lewis a very rich man. Humphrey Carpenter says: 'He was a sort of Clive James figure of his day an intellectual who had completely gone over to the pop side and made a great deal of money. Many of the dons at Magdalen were desperately jealous of that. The cosy college portrayed in the film was in fact absolutely poisonous.'

Lewis, an innocent about money, got into terrible fixes with the Inland Revenue. He was wildly generous to all sorts of people: as Owen Barfield, his friend and solicitor, recalls: 'He just scattered it. In the end I put that right by a Deed so that thereafter his gifts to individuals and charities came through me. Any of his friends were encouraged, if they knew of someone in need, to let him know.'

The writing of the seven Narnia books for children came about in a curious way, says Barfield. 'During her last illness, Mrs Moore was in an expensive nursing home and Lewis said he'd have to write a book to pay for it. But it was quite unthinkable to write a religious book in order to make money, so that was the start of the Narnia books.'

With the advice of Lewis's scholarly friends, Walter Hooper has seen the publication of 18 of Lewis's books since his death - 'in many cases works from learned journals which I found and collected; others, such as his diaries, had never been published at all'.

The final labour of love , which Walter Hooper is about to embark on, is the publication of the collected letters. After this, the whole body of Lewis's known work will have appeared in print.

(Photographs omitted)