“Walk the Line,” the new film about Johnny Cash, has all the requisite elements of a big screen biopic: a cotton field-to-high-cotton rise, family drama (a dead brother, unloving father, and nagging wife), and plenty of behind-the-music moments (amphetamine addiction, groupies, an extra-musical affair with June Carter). Still, the music – finely reproduced by Joaquin Phoenix and Reese Witherspoon – is the star of the show, just as Cash would have wanted it. “I’m not a savior and I’m not a saint, the man with the answers I certainly ain’t / I wouldn’t tell you what’s right or what’s wrong, I’m just a singer of songs,” he explained in one of the final recordings before his death in 2003.

But while “Walk the Line” covers the most dramatic period of Cash’s life – from his childhood in the late 1930s to his commercial peak in the late 1960s – it offers only a glimpse of his musical output. We see his early Sun sessions, where Cash was converted from gospel to his signature rockabilly sound (“steady like a train, sharp like a razor,” as Ms. Witherspoon’s June Carter puts it). We see the culmination of his outlaw persona at the 1968 Fulsom Prison show, which supplies the film’s climax. But we miss the distinctly American sweep of Cash’s material, which is the basis of his enduring legacy.

What made Cash stand out from his Sun Records colleagues was the maturity of his outlook. He was the least drawn to teenage truculence. At this early stage, his music already had the musk of manhood about it, soon to blossom into the particularly American stink of sweat and hardship. In its highly fanciful retelling of Cash’s audition at Sun studios, “Walk the Line” has Sam Phillips posing the challenge this way: “If you was hit by a truck, and you was lying out in that gutter dying, and you could sing one song, one song that would let God know what you felt about your time on earth, one song that would sum you up, what would it be?”

The mystery of Cash’s music is that, even with the standard set this outrageously high, it often lived up. His bedrock baritone sounded smooth on the surface, but it contained multitudes: the cry of the unrepentant killer (“Cocaine Blues”), the regret of the accidental one (“I Hung My Head”), and finally, the resignation of one who knows he’s done in himself (“Give My Love to Rose”).

It’s not as a rock ‘n’ roller that Cash is best remembered today but rather as a country singer of a particular stripe. Willie Nelson called him “one of the original outlaws,” and he was famously banned from the Opry stage for kicking out the footlights. Country, however, was also quick to claim him; in 1980, he became the youngest-ever Country Music Hall of Fame inductee. But no category can contain the man and his music. Johnny Cash was not a country singer so much as this country’s singer: He stands as the single greatest interpreter and embellisher of traditional American music since World War II.

In the late 1950s and early 1960s, Cash undertook a series of themed albums that mixed original compositions with covers of traditional songs. In 1959, by then signed to Columbia Records, he released “Hymns by Johnny Cash,” the gospel album that Sun hadn’t allowed him to do.That same year, he put out “Songs of Our Soil,” a collection of work, prison, and flood songs done folk music-style. Its highlight is “Five Feet High and Rising,” a song that recounts the day the levee broke at Wilson, Ark., and Cash’s father floated the family to safety on a boat fashioned from the front door. A year later, in 1960, he released “Ride This Train,” a tour through “the heart and muscle of this country” that included coal, lumber, and cowboy songs strung together with spoken narratives (the original vinyl had no breaks between tracks).

Outlaw songs, prison songs, train songs, flood songs, labor songs, gospel: This isn’t the output of a modern commercial artist but the American songbook reanimated and jumping off the page. And singing it connected Cash to a tradition that extended from Charley Patton to Leadbelly, Hank Williams, Jimmie Rodgers, and Woody Guthrie.

In the early 1960s , of course, many people were looking back to traditional material. But none belonged to it like Cash did, or it to them. He was somehow a living, singing example of an American folk type that was supposed to have vanished from the land – a T-Rex in a city park. When Bob Dylan first met him at the Newport Folk Festival in 1964, he is said to have just circled Cash the way you would an enormous tree and then, when he got all the way around, said simply, “Yah.” Here, for once, was a man who lived up to the legend.

A critical part of that legend is Cash’s charisma as a performer, best demonstrated on his live albums recorded before prison audiences: 1968’s “At Folsom Prison” and 1969’s “At San Quentin.” He shows that he understands his audience intuitively when he alternates a mournful “I Still Miss Someone” with a rip-snorting “Cocaine Blues”; longing and murder are closely linked. He wins them over with little rebellious acts of his own: “The show is being recorded for an album on Columbia Records, and you can’t say ‘hell’ or ‘s-‘ or anything like that,” he explains, not bothering to edit the words himself. It’s a measure of his credibility and connection with this audience that he can sing a song like “25 Minutes To Go,” which counts down to the hanging of a death row inmate, before an audience that might be facing that fate themselves.

Cash’s affinity for this crowd is no fluke. He was a vocal patriot and Christian, but his was a skeptical patriotism in line with Woody Guthrie’s. He allied himself throughout his life with the hard-luck and busted, and was ever-suspicious of power and those who wielded it. He performed for the troops in Vietnam, but at a Madison Square Garden show in 1969 described himself as “a dove with claws” before launching into the Weavers’ anti-war anthem “Last Night I Had the Strangest Dream.” An outspoken critic of the treatment of Native Americans, he recorded Peter LeFarge’s “The Ballad of Ira Hayes” and made it a staple of his shows.

His philosophy is expressed in what would become his theme song, “Man in Black”: “I wear the black for the poor and the beaten down / living in the hopeless, hungry side of town / I wear it for the prisoner who has long paid for his crime / but is there because he’s a victim of the time,” he sings, ” … well we’re doing mighty fine I do suppose / in our streak-oflightning cars and fancy clothes / but just so we’re reminded of the ones who are held back / up front there ought to be a man in black.”

As the capstone to his career, Cash partnered with Rick Rubin for his remarkable “American Recordings” series, which ran to four albums and an “Unearthed” boxed set of four discs. On it, Cash looks forward as well as back, bringing songs by U2, Nine Inch Nails, Tom Petty, Will Oldham, Tom Waits, and others into the American traditional canon. He was an incredibly subtle and powerful cover artist; his world-weary voice imbued songs with a poignancy that you often can’t distinguish in the originals. The best-known instance of this is “Hurt,” the Nine Inch Nails song that was made into a video featuring Cash. It shows him puffed and wrinkled, singing,”What have I become, my sweetest friend / Everyone I know goes away in the end,” as images of his more vigorous self flash by. It’s unrecognizable as the song that came from Trent Reznor’s lips.

There are many more examples like it in the collection. A personal favorite is “Singer of Songs.” At first this seems too modest an inscription for so great a man, until you understand the power Cash recognized in music. “I can take you for a walk along a little country stream / I can make you see through lovers’ eyes, and understand their dreams,” he sings, “I can help you hear a baby’s laugh, and understand the joy it brings / Yes, I do it with the songs that I sing.” By this more ambitious definition, he was a singer of songs indeed.

Should You See It?

“Walk the Line” is not a great film, but it gets credit for not trying to be one. There’s a temptation when dealing with the story of a legend like Johnny Cash to exaggerate the details and drama to make them worthy of the man. Under the deft direction of James Mangold, “Walk the Line” manages not to cross that one.

The early part of the film gives us a sense of where the music comes from, both geographically – the Edenic lushness of the Arkansas cotton fields is beautifully rendered by Phedon Papamichael’s supersaturated cinematography – and personally. Young John Cash grows up under the glower of his father (Robert Patrick), an Arkansas sharecropper who’s gotten no breaks from life and offers none to his sons – particularly John after the accidental death of his saintly brother, Tommy.

Looking for solace, John is pulled to the family radio like a frostbitten man to fire. And while he draws on his own hardship for the feeling in his music, he uses his uniquely empathetic imagination for the stories. “Folsom Prison Blues,” as the film shows us, was composed not in the penitentiary, but during a stint in the Air Force, which by all accounts felt to Cash like the same thing. (“I was in the Air Force for 20 years, from 1950 to 1954,” he would later quip.)

Back from the service, we witness his rise to fame as one of the Sun Records’ shock troops ushering in the era of rockabilly (white music’s answer to rock ‘n’ roll). Seeing Elvis, Jerry Lee Lewis, Carl Perkins, Roy Orbison, and Johnny Cash touring together, sharing the same cramped cars and exploding onto the same tiny stages, you get a sense for just how young, wild, and boundless the music was in the mid-1950s.

Joaquin Phoenix achieves the considerable feat of letting you forget that you’re watching an actor playing Johnny Cash and not the Man in Black himself, thanks both to the controlled low end of his singing voice (he and Reese Witherspoon perform all their own parts) and the cool swagger of his performance. Ms. Witherspoon’s June Carter is also compelling, if a bit too perky; despite the auburn dye, her “Legally Blonde” roots show through. The most convincing act of musical channeling, however, is Jerry Lee Lewis played by Waylon Payne (son of Willie Nelson’s longtime guitarist, Jody Payne). In a few stage-stealing scenes, he demonstrates why the Killer was once thought to be Elvis’s heir apparent.

The film resists making too much of Cash’s fame or influence or sound. Instead, in its second half, it tells the more modest story of his protracted (but not unconsummated) courtship of June Carter while both were otherwise married. It’s an unexceptional love story involving two exceptional people, and more credible for it.