The devil in Mr Osborne

Jim Callaghan was prime minister the last time Black Sabbath got the invite on to Top of the Tops. But early next month the four fiftysomethings, recently named as Kerrang! magazine's band of the millennium, will take the stage again, 30 years after they first formed.

Named after a B-horror movie, Black Sabbath were a band apart. Whereas Deep Purple and, a few years later, AC/DC, Motorhead and Iron Maiden were preoccupied with fast bikes and faster women, Sabbath were the province of the introverted male loner.

Ozzy Osborne could not sing - at least, not in the conventional sense - but no one will ever sound so convincingly god forsaken. Morrissey fans think that their man is the master of melancholy. But, while the depths to which the fed-up fop would plumb might be confined to the sartorial state of his weekend wardrobe, Osborne had more apocalyptic matters on his mind.

His baroque prophesies of doom ("Have you ever thought about your soul: can it be saved?"; "Leave the Earth to Satan and his slaves") were uttered against a backdrop of the uniquely heavy guitar sound of Tony Iommi: minimalistic and power-chord driven. With Terry "Geezer" Butler on bass, and Bill Ward (whose party piece was to tie up in dreadlocks, and then set fire to, a beard you could lose a badger in) on drums, the Birmingham Four were an alarming sight.

Their descendants include a host of death-metal bands - Biohazard, White Zombie and Megadeth are just three charming examples - but Sabbath weren't satanists, although, when they first appeared, it certainly looked - and sounded - like it. Their eponymous debut album was released on Friday 13 February; its tracklist and pseudo-poetical ramblings were printed over an inverted cross and one track - "N.I.B." - seemed to be an unequivocal plug for the sexual attractions of Hades' head of state.

The truth was more prosaic. Rather than standing for Nativity In Black, it transpired that it was not an acronym but, less diabolically, short for Nibby, a reference to Butler who had a magnificently large proboscis. And Osborne, when collared on tour by a fan who told him he needed help because he was heavily into black magic, could offer nothing more profound than: "Switch to Milk Tray," before hastily making his exit.

Although Sabbath traded on their devilish image when it suited them, the lyrics suggest that they were, if anything, a hippy band, and Satan a device with which to drive home their moral messages ("If you want a better world to live in/ Spread the word today/ Show the world that love is still alive").

Sabbath's strength, though, was that the themes running through their songs were all manna for the miserable, so resonant for who those were - or thought they were - disaffected and dispossessed. Fighting personal demons? Try "Megalomania". Fed up with the sheer torture of being? Listen to "Paranoid", their only hit single and their encore ever since. Disturbed by the supernatural? Scare yourself with "A National Acrobat".

When you consider Sabbath's obsession with naval contemplation, the remarkable thing about the new wave of heavy metal bands to come out of the United States in the 1990s is the number that cite Sabbath as an influence. The adolescent manic depressives who were into Sabbath were hardly the type to locate the exit to their bedrooms - much less leave the room, make friends, form a band and get a record contract.

Pantera, for example, successfully covered the relatively obscure "Planet Caravan" from Paranoid. But Sabbath's influence has spread well beyond its metal boundaries: Kurt Cobain famously said that he wanted Nirvana to sound like a cross between The Monkees and Sabbath. Sabbath's live act, too, is a benchmark: the notorious Cradle of Filth feature "a wall of fire direct from the depths of hell" (where else?) in their show and the pantomime excesses of Ozzy Osborne have been resurrected in the person of Marilyn Manson, whose penchant for fake blood, animals and satanic paraphernalia is well documented. More mainstream bands to be influenced include The Cardigans, whose latest album, Gran Turismo, has a distinctly harder edged sound than their previously fey offerings and who have recently revealed a predilection for Sabbath covers.

Black Sabbath lost their way towards the end. Technical Ecstasy (1976) and Never Say Die (1978) were the last two albums made by their original line-up; after Osborne departed Sabbath became just another heavy metal band. Osborne successfully went solo and periodically stirred the public's consciousness: doves and bats allegedly figured in his diet; his guitarist, Randy Rhoads, fatally crashed a light aircraft into Osborne's tour bus; and a teenage American fan allegedly took the title of Osborne's "Suicide Solution" - actually about alcohol addiction - at face value.

But now they're back. Love them, loathe them or laugh at them, no one has ever made it sound quite so certain that the world is about to end.

Black Sabbath play the Astoria, London, 5 Decemeber, and Birmingham NEC, 18 & 20 December