'He takes it very seriously and thinks the world's going to end at any minute. In a musical sense he's very dark'

As a natural outsider who learned early on to trust little beyond his instincts, Geoff Barrow of Portishead is a classic example of a musical pioneer who has gone against the grain - only to find the rest of the world coming with him.

He was born in Walton-in-Gordano, Somerset, but grew up in relative hardship in the small coastal town of Portishead, after which he named his band.

Portishead's 1994 debut, Dummy, remains one of the landmark albums of the 1990s, selling 2m copies in Europe alone. Released against prevailing trends at the height of Britpop, the album popularised what has been dubbed "trip-hop" or "the Bristol sound". A blend of slowed hip-hop grooves, Barrow's old skool scratching, soundtrack samples and (singer Beth Gibbons's) mournful, heartbreaking lyrics, Dummy has been widely copied but never equalled.

It was awarded the Mercury music prize in 1995 and Barrow received the respect of local peers Massive Attack and Tricky (whose classic 1995 debut, Maxinquaye, Barrow helped produce) and the city's original Bristol sound pioneer, Mark Stewart of the Pop Group, who sees Barrow as musically "flying the skull and crossbones of the pirate tradition" in a city that Portishead helped establish as a "haven of the avant garde". However, neither success nor acclaim has soothed Barrow's restless creative urges. He has said his only concern is making "interesting" music and he hates categorisation. "The whole trip-hop tag was nonsense," he once said, disowning the movement with which he is best known. "It was developed by people in London, and the people in Bristol just had to put up with it."

Barrow has always been a man apart. Growing up in the tough Portishead estates, he was never interested in the joyriding antics of his 14-year-old peers, preferring to obsessively programme music into his computer while existing on a diet of microwaved burgers.

In the 1980s he became absorbed with hip-hop, and then explored the music's roots in funk, soul and jazz, identifying with the hard edges and struggle inherent in black American music.

His first job in music was as tea-boy-turned-tape-op in Coach House Studios, where he assisted the fledgling Massive Attack and co-wrote a track for Neneh Cherry, Somedays, which hinted at the oncoming Portishead sound. Meeting (then pub singer) Gibbons on a training course, and later adding jazz guitarist Adrian Utley, Barrow was sharp enough to register Portishead as a company to avoid the attentions of the dole office.

Ferdy Unger-Hamilton, now Virgin Records MD but formerly the A&R man who signed Portishead to Go! Discs, remembers Barrow as a driven character who, months after sending him some demos, turned up at the record company office unannounced. "It was like he was checking us out," he says.

Soon afterwards, Unger-Hamilton regularly travelled to Bristol to hear a succession of tracks he realised were "amazing and revolutionary. [1994 smash] Glory Box was mind-blowing. I played it to the sales team and they were like, 'It sounds like a dog barking!' Some people thought it was mad and others just got it. I don't know if I've ever felt like that since." Unger-Hamilton was particularly struck by the bleakness and rage in the music, which he suspects lingers from Barrow's background. "He's almost angry about music. He takes it very seriously and thinks the world's going to end at any minute. In a musical sense he's very dark, but he's one of the nicest guys I've ever met. He's just a man on a mission."

A mission that Barrow has to feel is right, or else he isn't bothered. After a tortuous time recording a second album, 1997's Portishead, which just missed the top 20 in America, Barrow was left burned by touring and divorce. Portishead's once avant garde sound had also become fashionable, diluted by imitation. Thus Barrow took a back seat, setting up the experimental Invada label and producing Merseyside band the Coral. However, the new Portishead album, Third, sees him once again flying in the face of current music, and the band is touring this week for the first time in a decade.

"I think it's probably taken him this time to come up with something he felt was interesting," ponders Unger-Hamilton. "I've never met anyone as hard on himself over what he wants to do. They have musical rules which I don't understand - they're theirs, which makes it hard to make a record. The thing about Geoff - in fact all three of them - is the pain they put themselves through to make the music. That's where it comes from: from obsession."

NME editor Conor McNicholas sees Barrow as a "wilfully difficult musician. He's uncompromising and pure and we should feel privileged that he's still playing the releasing game to some extent. [Third] feels like a breath of fresh air compared to some of the manufactured crap slopping about at the moment. Many of us want true artistic passion and there's more than most could ever handle with Portishead."

The CV

Born December 1971, Walton-in-Gordano, Somerset

Work Musical artist and producer. Founder member of Portishead (1991-), who have sold more than 8m albums. Previously worked with Massive Attack and Tricky

Albums Dummy (1994), Portishead (1997), PNYC (live album, 1998), Third (to be released, 2008)

Singles Numb (1994), Sour Times (1994), Glory Box (1995), Cowboys (1997), All Mine (1997), Only You (1998), Over (1998)

Films To Kill A Dead Man (short film, 1994)

Awards Mercury music prize 1995, for Dummy