Late in 1914 four young Englishmen, just out of school, met and decided it was their mission to reform their country morally, through poetry. The odds of this quixotic enterprise’s success were ludicrously long to begin with, and they soon got worse. Within two years, two of the four were dead in Flanders. The third survived, abandoned the mission, and lived a normal life. The fourth became the most-read English-language poet of the 20th century, and his name was J. R. R. Tolkien.

This assertion would induce apoplexy in many a member of the Modern Language Association. “Most-read poet? What about Seamus Heaney? Or Sylvia Plath? Or Maya Angelou? How can Tolkien’s hobbitic doggerel and weird elvish pastiches be compared with real poetry?” Just the same, the claim may well be true, and would be even more likely if the competition were restricted to poems read for their own sake and not as part of a college requirement: Tolkien never had any help from the educational and literary establishment.

Of course, Tolkien’s high score is caused entirely by his poems’ being embedded in two of the most-read and best-loved prose fictions of the century, The Hobbit and The Lord of the Rings. One famous writer of fantasy confessed that when she finished The Lord of the Rings she felt bereft, because there was no more of it and she knew that she would never read anything so fulfilling again. She responded by starting to write her own fiction, and she was not alone: None of the fantasy stories now crowding the bookstores entirely escapes the mark of Tolkien, and several famous sequences started in similar ways, as emulations, continuations, tributes. Tolkien seeded authors, and he also created a market.

He left a vacuum, too. There was no sequel to The Lord of the Rings. It soon became known that there was a prequel, on which he had been working for many years, but when he died in 1973 it had still not appeared. Yet Tolkien, slow to publish though he was, never stopped writing and rarely threw anything away. The presses have been busy ever since with posthumous works, most of them (there are now almost 30) edited by his son and literary executor, Christopher. The latest, just released, is the long poem The Legend of Sigurd and Gudrún (Houghton Mifflin Harcourt, 384 pp., $26).

The first was a collection of translations of Middle English poems, including “Sir Gawain and the Green Knight.” The major event, however, was the appearance in 1977 of the long-awaited The Silmarillion. This is set in the same world as The Lord of the Rings, but much earlier. Parallels with the Old Testament are evident, though not dominant, and the book’s “First Age” ends with a kind of divine intervention to redress the evil caused by the elvish Fall. The book has been an inspiration to many, but a disappointment to many more: It gives The Lord of the Rings a frame, but it is a chronicle rather than a novel, full of names and genealogies, and often deeply sad.

Tolkien’s ambitions were, quite literally, epic. He was mesmerized by Norse, which was well-preserved in Finland: The complete lack of literary tradition in that country meant that oral tradition survived powerfully into the modern era. It was organized into the Kalevala by the 19th-century scholar Elias Lönnrot.

One of Tolkien’s goals was to be the English Lönnrot — but he was going to have to create his own raw material. This accounts for the bulk of the twelve-volume History of Middle-earth, edited by Christopher Tolkien between 1983 and 1996, and the two-volume History of the Hobbit, edited in 2007 by John Rateliff. On one hand, there is a string of false starts, deeply suggestive but never completed; on the other, attempts to “write into the gap,” fill in ancient non-completions. Early drafts fill up the Rateliff edition and most of the later Middle-earth volumes. They are for fans and scholars only, especially students of the creative process. But the first two of the twelve-volume sequence, published as The Book of Lost Tales 1 and 2, show Tolkien trying not only to re-create the hypothetical pagan mythology of his English ancestors, but also to harmonize it with his Christian and Catholic beliefs. He poured into these works his love of nature and his yearning for a world where life and beauty were not forever threatened — not heaven, not something spiritual, but an earthly paradise where the mallorn trees might grow.

One does not have to look very hard to see a personal motive — Tolkien lost his father when he was four, his mother at twelve, most of his friends before he got his first job — but it’s a personal motive shared by anyone who understands death. His theme is not death (though that is what he himself claimed), but something broader, and that is loss: loss of tales, loss of memories, and loss of friends, but also loss of beauty and diversity. The Lord of the Rings ends with some of the characters confronting — to use the modern terminology — habitat loss and species extinction.

Among the most interesting of the posthumous works is the fifth volume of “History of Middle-earth,” titled The Lost Road. This “unfinished tale” sprang from a conversation with C. S. Lewis sometime early in 1936. At that time both men had reason to feel unfulfilled. They had put every effort into becoming poets, and had gotten nowhere. Tolkien had had a scattering of poems printed, often anonymously and always in vanishingly “little magazines.” Lewis had had two collections published, which fell dead from the press. However, with astonishing resilience, they decided to change tack and write the kind of fiction they liked — since, after all, no one else was doing so. The toss of a coin gave Lewis the theme of space travel, and Tolkien time travel. The first volume of Lewis’s space-fiction trilogy came out in 1938, followed by its two sequels and the seven volumes of “Narnia.” But while Lewis never looked back, Tolkien got hung up. His idea seems to have been to tell a sequence of stories, set in different eras, connected by the names of the characters — which would recur disguised by the linguistic sound-changes of time — and by the theme of conflict between elf-friends and the followers of the Dark Lord. This effort survives as The Lost Road.

In 2007 Christopher Tolkien brought out the first fully completed Tolkien narrative since 1977, The Children of Húrin. This one is Tolkien’s Macbeth, a tale of a hero driven in the end to suicide by fate, or doom, or the malignance of the Enemy. It is animated by characteristically complex thinking about what we mean by “chance.” Traditional question in Oxford philosophy exams: What is a coincidence? This is Tolkien’s long answer, but few will be cheered by it, for the story is unrelentingly sad.

And now, in 2009, we have The Legend of Sigurd and Gudrún — a classic case of “writing into a gap,” the gap this time being the eight pages torn out of the main manuscript of Old Norse heroic poetry by some medieval vandal. Many have thought that the story of the Volsungs and the Nibelungs ought to have been the northern Homer, and there have been several attempts to re-create it, notably by Wagner. Tolkien’s effort is far more professionally competent than any other version. But written in the original meter, with the kind of archaic language much more acceptable in the 1930s, when it took shape, can it too reach a modern mass audience? Or is narrative poetry too extinct a genre to revive?

Having posed the questions, one might think again about those long-dead young men, with their strangely ambitious campaign for moral reform through the power of art. One of them, G. B. Smith, dead in 1916 of gas gangrene resulting from wounds, had written to Tolkien just before his death to hope that his friend would “say the things I have tried to say long after I am not there to say them, if such be my lot” (as it was). Did he? And is their campaign now at last having some effect, through the works of the one survivor?

The Australian science-fiction author Hal Colebatch has remarked that the enormous success of works such as The Lord of the Rings signifies “strong popular dissent” from the cultural orthodoxy and moral relativism that “bedevil modern Western society,” and this is dead right, but understated. Their success doesn’t just signify that dissent; it encourages, reinforces, and perpetuates it. How much effect have they had? Their readers are numbered in the hundreds of millions, many of them by their own account deeply moved; the viewers of the Peter Jackson movies number even more (and many of them will go on to read the books); and the books are available in scores of languages. Add to that the readers of the hundreds of Tolkien-inspired works, figure in the cumulative pressure of repeated statements of a traditional heroic ethos, allow for the fact that the Tolkienian ideology is not proclaimed but embedded — any way you figure it, it comes out as a lot. Sometimes the results are evident, as in the Tolkien-derived banners displayed by young Russians who resisted the abortive Communist coup in 1991. Sometimes the results have just soaked in silently. But the four young men have certainly succeeded, beyond the grave and quite literally beyond their wildest dreams. But then, as Gandalf says, “Even the wise cannot see all ends.” And, as he also says, “We must keep up our courage.”