Musical reputations come and go. A hundred years ago, Mozart was regularly dismissed as an exquisite lightweight while J.S. Bach occupied a respectable but somewhat forbidding place on the fringes of the repertory. Back then, neither of them was considered in the same league as, say, the revered opera composer Giacomo Meyerbeer -- who created such massive spectacles as "Les Huguenots" and "Le Prophete," now seldom performed and generally judged beyond resuscitation on those rare occasions when they do find a stage.

However, it is hard to think of any composer who has risen so high, fallen so low and then climbed so high again as Jean Sibelius. For most of his 91 years -- he lived from 1865 to 1957 -- Sibelius was accepted as the natural heir to the symphonic legacy of Beethoven and Brahms, not only admired by fellow musicians but enormously popular with the public. His native Finland issued a postage stamp to commemorate his 80th birthday; closer to home, when the Soviet Union invaded Finland at the beginning of World War II, a relief campaign in the United States fashioned an effective fund-raising poster. It bore the image of Sibelius and four simple words -- "I need your help."

Even then, however, a strong reaction against Sibelius had begun in musical circles, one that intensified during the 1950s and '60s and began to relent only in the late 1970s. With the exception of a few pieces ("Finlandia," above all, but also "The Swan of Tuonela," the "Karelia" Suite, the Violin Concerto and, to some extent, the Second and Fifth symphonies), his music fell from grace. Proper modernists dismissed him as an outright reactionary for the consonant harmonies and romantic sweep of his most familiar music. The composer Virgil Thomson, who was chief critic for the New York Herald Tribune from 1940 to 1954, took every opportunity to cut him down. "I realize that there are sincere Sibelius-lovers in the world," Thomson sniffed in 1940, "though I must say I've never met one among educated professional musicians." The French composer and conductor Rene Leibowitz went so far as to write an intemperate pamphlet called "Sibelius: The Worst Composer in the World." (And what, one cannot resist asking, has Rene Leibowitz done for us lately?)

In any event, as the century comes to a close, Sibelius has been triumphantly rehabilitated. He is once again a hero to many composers, ranging from the onetime British avant-gardist Peter Maxwell Davies to such post-minimalist Americans as John Adams and Ingram Marshall. Moreover, there are an enormous number of good recordings of his work available, with new releases coming along every month. Thomson used to refer to the Russians and Scandinavians as "cold climate" composers, and now the ultimate cold-climate composer is positively hot.

Jean Christian Sibelius was born in Finland on Dec. 8, 1865. He played the violin from an early age and, like many composers, was writing music before he formally "knew how." A rather stern-looking young man, his appearance only grew more austere as his hairline receded. He studied in Berlin and Vienna before returning to Finland, where he immersed himself in the movement for Finnish independence from czarist Russia. (Finland has, at different times, been forced to fight not only the Russians but also the Swedes and the Danes to hold on to its national identity.) Nordic legends and episodes from the great Finnish epic The Kalevala figure in much of the composer's music, and he became a proud nationalist. Indeed, Baker's Biographical Dictionary of Musicians has called Sibelius the "last representative of 19th century nationalistic Romanticism," but he is much more than that, which is why he fascinates and perplexes us today.

There are two things to be said straightaway about Sibelius. First, he is terribly uneven (much of his chamber music, a lot of his songs and most of his piano music might have been churned out by a second-rate salon composer from the 19th century on an off afternoon). Second, at his very best, he is often weird.

For example, the Symphony No. 6 (1923) is one of the century's most curious masterpieces -- serene, beatific, almost Mozartean in its clarity and grace, suffused with warm winter light. It is rarely played, has little to do with anything else Sibelius ever composed (what to make of the second movement, that long series of musical question marks?), and its interpreters have a habit of trying to turn it into Tchaikovsky or the more traditionally "romantic" Sibelius Symphony No. 5 or something else that they might recognize -- trying, in other words, to make it fit into a pattern. And it doesn't fit -- which is not at all to say it doesn't work.

Because Sibelius was such a quirky and intensely personal creator, he has had remarkably few disciples. The other great composers who worked through the first quarter of the 20th century -- Richard Strauss, Arnold Schoenberg, Igor Stravinsky -- are easier to imitate because their music has immediately identifiable traits and generally obeys certain laws (the composer's own, more often that not). And so a whole school of French music was able to spring directly out of Stravinsky, while every American university had a mini-Schoenberg or two in residence throughout the 1960s and 1970s.

But how does one write imitation Sibelius? Even Sibelius himself couldn't do it, and he left no new "laws." None of his last five symphonies has much in common with any of its neighbors; philosophically speaking, they all start pretty much from scratch. His music cannot be codified and it is not easy to explain -- what would seem meandering and digressive in other composers comes across as either intrepid exploration or sheer strangeness in the best of Sibelius. There is nothing academic in his nature; he did not invent a compositional system (as did Schoenberg), nor did he attempt to perfect any specific "style" (such as the neoclassicism of middle-period Stravinsky). Indeed, for the most part, his musical syntax was not particularly unusual; rather, he used a common language to say uncommon things.

A great Sibelius performance will likely be as contradictory and surprising as the scores themselves -- simultaneously wild and dramatic, Spartan and dignified, "passionate but anti-sensuous," as the late Glenn Gould once described it. And despite the large symphonic forces for which his best music was written, silence has a disproportionate importance in the work of this most sonorous of composers. If silence can be defined as an absence of sound, it may be helpful for the novice, when coming to Sibelius, to consider his music a temporary respite from quietude. The image of Sibelius as a brooding poet of the spare, near-motionless, unpeopled North is fairly hackneyed by now, but it is no less true for all that.

Among the many Sibelius recordings available today, one stands out as a spectacular bargain: the complete set of the symphonies, set down in the late 1970s, featuring Sir Colin Davis and the Boston Symphony Orchestra on the Philips label. Not only does this provide listeners with most of the essential Sibelius (in addition to excellent and idiomatic performances of the symphonies, it includes the Violin Concerto with Salvatore Accardo and the tone poems "Finlandia," "The Swan of Tuonela" and "Tapiola"), but it does so on four specially priced compact discs that most retailers sell for less than a full-priced two-CD set.

Other editions that ought to be considered include the vibrantly emotive cycle conducted by Leonard Bernstein with the New York Philharmonic (Sony Classics -- avoid his late, turgid renditions with the Vienna Philharmonic on Deutsche Grammophon), Paavo Berglund with the Helsinki Philharmonic (EMI Classics) and a startlingly persuasive recent set with Jukka-Pekka Saraste with the Finnish Radio Symphony Orchestra, issued last year on Finlandia.

Those listeners in search of individual symphonies have a spectacular range of recordings from which to choose (there are at least 50 renditions of the Symphony No. 2 alone). If you are at all fond of Sibelius, it is also advisable to pick up his early symphony-cum-oratorio "Kullervo," a panoramic treatment of Finnish lore for large orchestra and chorus that dates from 1892 and was suppressed by its composer during his lifetime. Indeed, I find it more than the much-later Symphony No. 1, which is a lot like Tchaikovsky but not so personal and assured. "Kullervo," in the original Finnish, is available in a bang-up performance by the Los Angeles Philharmonic, under Esa-Pekka Salonen on Sony Classics.

I have no special recommendation for the Symphony No. 1; Vladimir Ashkenazy on London, Bernstein on Sony and Herbert von Karajan on EMI Classics are all more than acceptable. My favorite recording of the Symphony No. 2 is a thrilling old Pierre Monteux disc with the London Symphony Orchestra, once available on RCA Victor, later on London, and probably set for CD release in the not-so-distant future. The insistently repeated theme in the last movement can either be beguiling or terrifying; most conductors opt for charm, but I prefer the suggestion of fierce Northern wind (Toscanini, on RCA, does a suitably unrelenting job here but the sound is dated). Bernstein with the New York Philharmonic is a little too lilting in the finale for some tastes, but he does bring an eerie ferocity to the second movement as well as his usual bristling excitement throughout. One might also consider the new James Levine performance with the Berlin Philharmonic on DG and the recording Herbert Blomstedt made with the San Francisco Symphony on London.

After the Symphony No. 2, we find a new Sibelius in place with each new symphony. The No. 3 is sweet-tempered, folkish and not immediately arresting (it is probably the least played of the symphonies). Yet it inspires affection among many who know it well, and it is very beautifully rendered by the London Symphony Orchestra, under Davis on RCA Red Seal, with a strong, solid version of the Symphony No. 5 as its disc-mate; when this new cycle is complete, it may be the edition of choice -- the first installments in the series have been even more authoritative than the versions Davis made with Boston.

The Symphony No. 4 is as baffling and forbidding as any work in the 20th-century repertory. I've loved this piece for almost 20 years, play it incessantly and still don't think I understand it fully. Bleak, spare, nothing if not mysterious, the symphony has been likened to a sort of musical cubism and, as such analogies go, that's a pretty good one (the first movement, in particular, is built block by sonic block, with an absolute minimum of padding). Oddly enough, the smooth, creamy textures that von Karajan elicited from the Berlin Philharmonic suit it perfectly; they complement the work's strangeness rather than dulling or drowning it. I prefer von Karajan's mid-'70s recording on EMI Classics to both his later (and earlier) readings on DG. Saraste and Blomstedt are also particularly fine in this symphony.

The No. 5 marks a partial return to form. "God opens his door for a moment and His orchestra plays the fifth symphony," Sibelius wrote in his diary during the process of composition. This is noble, affirmative, Heaven-storming High Romanticism, without any self-consciousness (and certainly without any trace of the modernist fragmentation we found in the No. 4). Here, again, von Karajan is excellent (any of his several recordings) but Bernstein is also riveting, as is Simon Rattle on EMI Classics. Indeed, for whatever reason, there seem to be more satisfactory recordings of the Symphony No. 5 than any of the others. For a different take on this piece, pick up Osmo Vanska's recent album for Bis Classics with the Lahti Symphony Orchestra -- an early, four-movement version that was quickly (and wisely) rejected but makes for a fascinating comparison.

We have already discussed the Symphony No. 6; my favorite recording is the first one made of it, dating from 1934 with Georg Schneevoight and the Helsinki Philharmonic. Tranquil and radiant, somehow conveying a humble and profound gratitude for the experience of life and living, it is now available on the Finlandia label (distributed by Warner) on a disc called "Historical Sibelius Recordings." Among more modern recordings, Davis and the London Symphony on RCA can be recommended.

To this taste, the Symphony No. 7 marks a falling-off after its three predecessors -- it seems an elaborate jaunt around the periphery of a prepared catharsis that never quite occurs. But many will disagree (the British critic Cecil Gray thought the Sibelius Seventh the most perfect symphony ever written). In any event, Bernstein and the New York Philharmonic do it up proud -- gorgeous, caloric string textures and lowing, majestic trombone chorales.

Setting aside the symphonies and the best of the tone poems, the other essential large Sibelius work is the Violin Concerto (which dates from roughly the same period that produced the Symphony No. 4 and the eerily fascinating "Luonnatar" for soprano and orchestra and shares some of their luminous darkness). Two historic performances of the Violin Concerto have been recognized as classics all along -- the first recording by the late Jascha Heifetz (accompanied by Sir Thomas Beecham; don't bother with the later version on RCA Victor with Walter Hendl and the Chicago Symphony) and the somewhat less dramatic but more expansive and graceful recording by the short-lived French violinist Ginette Neveu. Both of these are available on EMI Classics. Among recent recordings, the Russian emigre Viktoria Mullanova's disc with Seiji Ozawa and the Boston Symphony Orchestra on Philips is terrific -- and it shares a disc with an equally valuable performance of the Tchaikovsky Violin Concerto.

Sibelius left four string quartets, of which only one is a fully mature composition. "Voces Intimae" -- "Intimate Voices" -- is a sort of sustained study of various shades of musical gray, quite beautiful in its measured way. The readings by the Guarneri and Juilliard quartets (on Philips and Sony, respectively) are too unwontedly dramatic for this very static music; I suggest one of the Finnish quartets, such as the Sibelius Academy Quartet on Finlandia or the Voces Intimae Quartet on Bis.

Among the smaller works is bass-baritone Tom Krause's carefully chosen selection of the songs on Finlandia. And Glenn Gould's album of the otherwise unremarkable Sonatinas for piano has a fascinating quirk that should make it irresistible to anybody interested in Gould and his philosophy. He recorded the music with several microphones to capture the same performance from different vantage points and then used the tapes in the same way a movie director might coordinate a roomful of cameras. And so one phrase might be in "close-up" -- recorded only a few inches from the sounding board of the piano -- and the next phrase might be far away, a "long shot," with the piano in the sonorous distance. Whatever else this recording may be, it's unique; Gould never tried this experiment again.

Sibelius basically stopped composing around 1930, more than a quarter-century before he died (his last major work is the ruminative "Tapiola"). For years, there were rumors of an in-progress Eighth Symphony, but nothing turned up after the composer's death; there is some evidence to suggest that the symphony was written and then destroyed. Whatever the case, this "silent period" has been the subject of much speculation. Did Sibelius lose his gift? Was he debilitated by alcohol, of which he was very fond? Was he inhibited by his enormous reputation or, perhaps, by the innovations of young composers? Had he simply said his piece?

Another Sibelian mystery -- as compelling as the enigmas we find in his music. CAPTION: Composer Jean Sibelius: Once hot, then cold and now hot again. CAPTION: Last of the romantics? Twentieth century giant? Or both? Jean Sibelius early in his long career, above, and in 1950. CAPTION: Above Sibelius and Finnish official with crates of food sent from America to Finland during World War II. Below: The 89-year-old Sibelius with conductor Eugene Ormandy. CAPTION: Recordings by Sir Colin Davis, above, Jascha Heifetz, below, are strong pro-Sibelius arguments.