John Martyn played many roles in his three score years. Curly-haired troubadour, spaced-out innovator, thug, fisherman, wizard, wastrel, lover and fighter. When Linda Thompson first met him in the mid-Sixties, all those lives still lay before him. He was merely Iain McGeachy, teenage paper boy, pounding the Merrylee beat in his school uniform.

“He was my paper boy, and devastatingly good looking, even then,” says Thompson, the former wife and musical partner of Richard Thompson, and folk royalty in her own right. “He always said, ‘I’m going to be terribly famous, because I’m fabulous!’ He was preternaturally confident, I never met anyone so sure of himself till Rufus Wainwright, decades later. It unnerved people. From a young age, John divided people. He was different from other people in Glasgow, he was very free.”

Ten years gone this month, John Martyn is Scottish music’s great gallus maverick. Though he was born in Surrey and died in Ireland, Martyn was formed in Glasgow. When his songbook is celebrated at Celtic Connections tomorrow by artists including Paul Weller, Eddi Reader and Eric Bibb, it will have the resonance of a final homecoming.

Born Iain David McGeachy on September 30, 1948, in New Malden, Martyn was raised by his father and grandmother in a sprawling two-storey tenement at 10 Tantallon Road in Shawlands. He was two when his parents divorced. His mother Betty remained in Surrey, remarrying twice and having two more children. He visited her during summer holidays, but her daily absence bestowed a raging insecurity which lasted a lifetime.

When I spoke to Martyn’s first wife, Beverley Martyn, she recounted stories of him “writing to his mother and never getting any reply. Many letters were found that his mother had kept. ‘Dear mummy, I miss you so much, why don’t you write back?’ ‘I love you, when can I see you.’ It was heartbreaking. He was wounded from the beginning. Maybe if he wasn’t like that we wouldn’t have the music, with such depth of feeling.”

When I interviewed Martyn in 2005, he said, “I’m quite sure that any flaw in my character has to do with the divorce of my parents. I’m very sure of that.”

Yet he did not lack love. He was surrounded by doting cousins and aunties; his gran, Janet, was strict but adoring. In Tantallon Road, music was a constant. His parents had been light opera singers, he said, all “hampers and stage make-up. Not really my caper.” His father, Tommy, “sang opera for the troops,” says Martyn’s cousin, Fiona McGeachy. “He was on the radio during the war. At my granny’s place, the aunts and uncles ended up in the sitting room, the fire on, granny playing the piano and everyone doing their party piece.”

Music was one inheritance. There were others. Martyn once told me he was bequeathed a sense of decency from his father and a wandering morality from his mother, not to mention a weakness for alcohol. Billy Connolly befriended Martyn on the Glasgow folk scene. “He was still Iain McGeachy then,” says Connolly. “He was scared he’d become alcoholic, because his father was alcoholic.”

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Martyn once said: “It runs in the family, from my grandmother on down. My old man went at 84 and he was still drinking, big time. At first, I drank because I was nervous performing, then the lifestyle got hold of me.”

This was all to come. At Shawlands Academy, Master McGeachy was an outgoing, exceptionally bright student. In 1963, he was one of three members of class 3B1 chosen to represent the school in the TV quiz show, Round Up. He was selected for a pilot project to study both Latin and French, and in 1964 was the top English student. Though natural university material, he was already lost to music. “We hung out at a cafe in Calder Street, smoking and playing the jukebox,” says Linda Thompson. “Later we’d go to folk clubs together and have fun. He was instantly quite impressive.”

He strolled around town in a sheepskin coat with a fur collar and stripey jeans, guitar in hand. By 1966 he was making forays to the Glasgow Folk Centre on Montrose Street, Clive’s Incredible Folk Club on Sauchiehall Street, the Scotia on Stockwell Street and the Crown in Edinburgh. His patron was the Falstaffian folkie Hamish Imlach, who allowed Martyn to perform before his own sets, and who grumbled good-naturedly about the curly-haired kid who left sweetie wrappers in his car.

From Imlach he learned stage presence, a robust finger-picking guitar style, and how to live large. Good food, and plenty of it. Open house, with various intoxicants on tap. Come all ye, and last man standing wins. Wit and staying power were precious metals, prized above all things. “John had a wee bit of a swagger about him that was rare in one so young,” says his contemporary, singer-songwriter Rab Noakes. “It wasn’t anything obnoxious, he was just quite cool and aware of his capabilities. From an early age he knew how to hold people’s attention.”

On stage, he had good patter and a few flashy tricks. “He did an instrumental on the guitar using the capo, he’d slide it up and down, going up a half tone each time,” says Billy Connolly. Inspired by Bob Dylan, he was already writing. Connolly recalls Golden Girl, which appeared on Martyn’s first album. “I wandered in the green stream that meanders round my mind,” he sings. “Ah, he was amazing.”

A young man in a hurry, by spring 1967 he had moved to London. Rechristened John Martyn at his manager’s suggestion, he became a boisterous fixture at folk hubs Les Cousins and the Troubadour, and was quickly signed to Island Records. His debut album, London Conversation, arrived in late 1967. Martyn would walk through Soho with the record tucked under his arm. “It all happened quite quickly,” says Fiona McGeachy. “We were awful proud of him. I would lie and listen to his music at night on my gramophone. I really worshipped him.”

London was about transformation. His rather refined Glasgow south side accent quickly came under assault. Depending on the context, he could sound like a Cockney barrow boy or a hard case from Barlinnie. “He would revert, it was very schizophrenic,” says Linda Thompson, who had also moved south. “It’s partly a musical thing, picking up on the tone, and partly a deep rooted insecurity to be liked and accepted. Being John, he took it to staggering lengths. He had different personalities for different things.”

His music also evolved. In 1969, aged 20, he married fellow singer Beverley Kutner, becoming step-father to her baby son Wesley. The couple made two modestly successful albums together, but Martyn was uninterested in sharing the limelight. In 1971, he embarked on a streak of remarkable solo albums, often in tandem with his closest musically ally, former Pentangle double bassist Danny Thompson.

Moving out of the folk clubs onto the university circuit, he music became an exploration in sound as much as song. His vocals stretched and coarsened, taking on the cadences of the saxophone. “He had a very pretty voice, which irked him a bit,” says Linda Thompson. “He wanted to sound rougher.” He experimented with Echoplex, a tape delay effect which enabled him to coat his acoustic guitar in layers of spiralling reverb, a technique since popularised by KT Tunstall and Ed Sheeran. Floating between folk, jazz, soul and blues, the music was bewitching, but he often appeared hellbent on subverting its beauty. “He’d sing a beautiful song like Couldn’t Love You More, he’d be way into it, and after he finished he’d belch,” says Danny Thompson. “He didn’t want you to see his soft underbelly.”

Bless The Weather, Solid Air and One World are masterpieces, but virtually everything Martyn released between 1969 and 1980 is essential. There was plenty of acclaim, but no hits. He followed the music rather than the money.

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During this period he returned home frequently, to work and play. When he and Danny Thompson visited Glasgow, they’d stay at Tantallon Road rather than a hotel. “We’d wake up early, breakfast was porridge, prepared by his wonderful, much loved gran,” the bassist recalls. “Then off in a black cab for a ride out to a country spot where we jumped over the dry stone wall, then across the fields to a shallow stream. He flicked his bamboo fishing stick until six brown trout lay on the bank. Back across the fields and into the nearest pub, two pints, and a return cab to number 10. ‘Hello, Gran, trout for tea!’ A bit of banter then off to the local bowling green. We’d play and gamble with serious competitiveness. It was the same with snooker. Then we’d ride into Glasgow and enjoy the Scotia Bar, or the Victoria. We’d have a play and get completely pissed and share the oxygen.” He laughs. “I don’t want to make out that it was very mumsy. We used to have serious fights as well. I’ve been nutted by him.”

During this time he and Beverley had two children, Mhairi and Spencer. The family moved from Hampstead, in west London, to Hastings, and finally to Heathfield, in east Sussex. As the music soared, so Martyn’s behaviour became more extreme and unpredictable, exacerbated by alcoholism and hard drugs. “A personality was beginning to appear that was more abrasive,” says Noakes. “The accent changed, there was a bit of, who are you trying to be? Split personality is too strong. John was maybe a series of inventions of characters.”

There is a tendency to romanticise Martyn, but some things should not be airbrushed. The loveable rogue persona played out on stage and in bars could curdle into something far nastier, especially behind closed doors. He was not just an unfaithful and largely absent husband; he was also an abusive one. When Beverley fled the marriage in 1979, she feared for her life. “I slipped my feet into my son’s boots and ran to the police station,” she told me. “I could never go back, but it left me relying on state benefits. It was hard. He mistrusted women and so treated them really badly, physically and mentally.”

Newly divorced, Martyn bunked with Phil Collins while they worked on the rawly emotional Grace and Danger. Afterwards, he briefly moved back to Tantallon Road, where his father cut an increasingly eccentric figure. At one home town show, Tommy exited halfway through, informing his son loudly that he was leaving. In 1982, Martyn settled in a cottage by the church in Roberton, a village in the Borders.

By the time I caught up with him in 2005, he was in rough shape. Following the end of one serious relationship, he had walked away from a baby son, severing all contact. A second physically abusive marriage had ended in divorce. Locals in Biggar, the nearest town to Roberton, had grown accustomed to him acting out in the Elphinstone Hotel. “People are somewhat astonished at the amount I drink, but it’s just a matter of practice,” he told me. “I’m not proud of it at all, if you’re not careful you can make a right arse of yourself, but I’m by no means ashamed of it either.”

He had gone bankrupt, lost his house, broken his neck, and split his head open while swimming. The determination to experiment musically remained undimmed, but the muse had become a less attentive mistress. Most significantly, in 2003 his right leg was amputated below the knee, when septicemia ravaged his system. By then, Martyn was living in the Kilkenny town of Thomastown with his partner Teresa. In the beer garden of his local, Carroll’s, as he outlined his affinity to Buddhism, he drained pints of cider into which he periodically dumped tumblers of neat vodka. There was certainly wildness lurking there, but also courtliness, wit, erudition and refinement. Weighing over 20 stones, scarred and battered, he walked with the aid of a prosthetic and a huge staff, but any hint of pity was swiftly stamped on. “I’ve had a wonderful time,” he said. “I can’t argue at all about what life’s dealt me.”

Martyn continued to tour in a wheelchair even as his health deteriorated. He died of pneumonia on January 29, 2009, aged 60, weeks after being awarded an OBE. It was a rare official accolade for the ultimate musician’s musician, lauded by Eric Clapton, Robert Smith and Dave Gilmour, but forever on the cult side of the mainstream. “For whatever reason, he’s not recognised as much as you might expect for someone who has had moments of genius and created his own pathway,” says Donald Shaw, artistic director of Celtic Connections. “He’s much loved, but in an underground way.”

Martyn always professed he was happy being the connoisseur’s choice. Linda Thompson isn’t so sure. “He thought he was going to be famous,” she says. “I think he aspired to that. Why wouldn’t he? He was very handsome, he was brilliant – but it didn’t take, and I think he was puzzled by that. He didn’t help himself, of course, with that slightly self-destructive Glaswegian thing. Billy Connolly had it, too, but he drew back from it. My friend Gerry Rafferty had it in spades. John shot himself in the foot constantly.”

Is Martyn’s career, so replete with youthful zest and promise, ultimately a story of wasted opportunity? Danny Thompson – who will be anchoring the house band at Celtic Connections – shakes his head. “No. I understand other people feeling that, but you have to be true to yourself and live your own life. John never pretended to be anything that he wasn’t. People hear all these different stories and say, What was John really like? If you really want to know what he was like, listen to the songs. That tells you everything about the man. It’s music of the heart.”

Grace & Danger: A Celebration of John Martyn, Royal Concert Hall, Glasgow, January 27