There have been well over eight million YouTube views of Johnny Cash's Hurt video.

It shows a man who looks spent, for whom every word is an effort to express. His pallor is that of over-milked scrambled eggs. He strums a guitar, sits at a piano looking lost, pours wine from a goblet on to a table groaning with food. He looks close to death, a feeling emphasised by the video's location, the House Of Cash Museum, which, a sign says, is "closed to the public".

Cash was then 69 but he looked a lot older. As the video unfolds it revisits scenes from his life: his childhood home in Dyess in the Mississippi delta, the flood of 1937 which ruined the lives of many, a framed photograph of his mother, Christ on the Cross, trains and buses and state penitentiaries. Meanwhile, Cash, looking like he's been carved for a country and western music version of Mount Rushmore, sings: "I hurt myself today/To see if I still feel/I focus on the pain/The only thing that's real." Two years later, in 2003, he was dead.

The Hurt video really said all that need be said about Johnny Cash. Even by the standards of the music industry, his was a life lived on the edge. The wonder is that he didn't die much sooner. Certainly, there were numerous times when it looked like he'd had it, when the booze and drugs got so out of control that his heart wasn't inclined to go on pumping.

On occasion he lost his voice, the result of habitual use of dexedrine. He'd go on stage and no more than a whisper would emerge. It happened most embarrassingly at Carnegie Hall in New York in 1962, when all he could do was mouth the words of his songs. "All the people were hearing from me was my guitar," he said.

He was then 30 and in danger of becoming one of those C&W legends, like Hank Williams and Charlie Poole, who wouldn't see 40. Self-destruction seemed to be in Cash's DNA, a consequence of his addictive personality. On top of which, he was riven by guilt, imbued as he was from birth by what Robert Hilburn describes as "the literal message of heaven and hell, salvation and eternal damnation".

The Lord he and his family worshipped was one who took away as much as he gave, and poverty was endemic. Cash was a four-year-old when he started to carry water to the rest of the family, six when he was expected to pick cotton. Music was one of the few distractions from such back-breaking labour.

Cash liked gospel music, which remained with him throughout his seven decades, and the songs of Jimmie Rodgers, aka the "Singing Brakeman", with his tales of lonesome men travelling the length and breadth of the country in railway boxcars. It was music at its most escapist.

Cash's first true mentor, however, was his older brother, Jack, who seemed destined for a career in the ministry. "Everyone in the family," writes Hilburn, "looked upon Jack, who was named after the heavyweight champion Jack Dempsey, as the golden child." Jack was so good he didn't rat on Johnny when he caught him, aged 10, smoking a cigarette, another habit he never quit. But when Jack was just 14, he died when the saw he'd been using to cut oak logs ripped open his stomach. No-one was more effected than Johnny, who remembered how Jack had refused to judge him even as his father talked about "the evil stage, the evil showbusiness".

In Cash's hinterland, forgiveness and censoriousness walked hand in hand. As a teenager, he was studious and Bible-loving, steering clear of alcohol and girls, fearful of being led into temptation. As America mobilised for war with Korea, he joined the air force and shone as a radio interceptor.

By the time he was due to be posted to Germany, he had fallen for 15-year-old girl called Vivian Liberto to whom he promised to be faithful. Cash was good at making promises; not so good at keeping them. After he and Vivian married, Cash wrote her I Walk The Line, a paean to fidelity, to prove to her he was not like other country and western singers. If only it were true.

Cash's music career has perhaps three distinct phases. The first was when he signed for Sam Phillips of Sun Records, which was also the original label of Elvis Presley and Jerry Lee Lewis. Out of those years came "boom-chuck-a-boom" songs such as Hey Porter, Folsom Prison Blues, Get Rhythm and I Walk The Line, which would remain constants in Cash's repertoire. As his fame grew, however, he was poached by Columbia Records, a period marked by his dependence on stimulants, the need for them exacerbated by constant, exhausting touring.

Though still popular among C&W devotees, it looked like Cash would fall victim to a combination of Beatlemania and Flower Power which engulfed the 1960s, and to an extent he did. What saved him from oblivion was a concert at Folsom Prison in 1968 when he greeted the inmates with "Hello, I'm Johnny Cash" before launching into Folsom Prison Blues. The following year he gave another concert to prisoners, this time at San Quentin, which was filmed - and where he came close to causing a riot by declaring, "San Quentin, I hate every inch of you."

Cash's third phase was the most unlikely and some, including myself, would argue his most meaningful. Its unlikely inaugurator was Rick Rubin, a producer who had previously done wonders for Public Enemy and the Beastie Boys. Looking more like a Hell's Angel than a season ticket holder at the Grand Ole Opry, with a bald pate, long hair, and an unruly beard, Rubin was what Cash called "the ultimate hippy". Amazingly, the pair hit it off and Rubin persuaded Cash to return to his roots. Together they recorded a series of albums of standards and new songs which brought the veteran artist a huge new audience and the acclaim of his peers.

Though by now his voice was weak, Cash injected immense depth and emotion into songs that simultaneously wrench the gut and make the heart sing. One such was The Man Comes Around which, remarks Hilburn, "had been haunting Cash for years". Its subject, Christ's second coming, is not one normally associated with popular music. Ironically, it felt as if it was Cash who had been resurrected.

Hilburn, who used to write for the Los Angeles Times and knew Cash back in the day, has produced a moving, respectful and sympathetic biography. In particular, he handles sensitively and unjudgmentally the break-up of Cash's marriage due to his affair with June Carter, whom some smug country fans compared to Yoko Ono. Eventually, Cash and Carter were married and though the relationship was combustible, it survived, a belated gift from a God who has always had to work overtime in Nashville.