On April 30, Willie Nelson turned 70, celebrating with the release of his latest greatest-hits collection. The Essential Willie Nelson (Columbia/Legacy), a two-CD set, has an intriguing 1970s-vintage cover shot that sets exactly the right tone for forty years of selective tracks. Nelson’s unkempt long red hair and scraggly beard frame his thin, almost Bob Hope nose. His mouth twists slightly, a smile just short of a sneer, in sardonic, knowing reaction to the world behind the camera. His eyes, couched in wrinkles and bags, stare straight and deep into the lens, and suggest hard-to-fathom distances and recessions at the same time as they focus you into connecting. This interaction, evasive, seemingly casual, direct and subtle, represents the essence of Nelson’s sly, almost unobtrusive art.

The Essential Willie Nelson demonstrates once again that the Red-Headed Stranger’s nonchalant, gospel-flavored, jazz-inflected voice and guitar have remained essentially themselves for decades despite a wild variety of musical backdrops: bare-bones string bands, sleekly glossy Nashville productions, twangy 1970s Outlaw country-rock, jazzy standards with strings, gospel-laced soul.

Maybe that breadth helps explain why Nelson’s recurrent duets with Ray Charles are almost always so charged–and so much fun. After all, only Charles and Bob Dylan have traveled as sure-footedly across as far-flung a constellation of genres and expectations as Nelson has and still remained themselves; Charles and Nelson have long shared material and appearances. (A 1984 show at the Austin Opera House, captured on The Willie Nelson Special [Rhino Home Video], features excellent versions of “Georgia on My Mind,” “I Can’t Stop Loving You” and the old hillbilly fave “Mountain Dew.”) Part of this odd couple’s magnetism stems from the fact that they represent opposite poles of the American spectrum. Charles, the consummate besuited black professional trained in the tough world of low-rent, postwar r&b, whose nonpareil voice influenced countless singers, is a hard-bitten recluse who heads a thriving business dynamo and a drilled band. Nelson, the white country-music renegade who tried pig farming for a while when his career soured, comes onstage in hippie-cowboy-Indian costume, calls his band Family and is the epicenter of the self-consciously laid-back Austin music scene (his disciples include Townes Van Zandt, Lyle Lovett, Joe Ely, Jimmie Dale Gilmore and alt-country outfits like Uncle Tupelo) he helped seed and feed for the thirty years since he first strode onstage at Armadillo World Headquarters. Even on an off night, Charles can suddenly burst whatever frames the ragged, churchy elasticity of his scuffed and soaring trademark voice. Nelson stays introspective: Lacking Charles’s explosive interpolations, he subsumes his surroundings, enticing the audience into his voice’s unexpected contours.

Think of Charles as Louis Armstrong’s direct descendant, and Nelson as a cross between Bing Crosby, Jimmie Rodgers and Woody Guthrie. Their duets are like oil and vinegar, always about to separate if not stirred up, delicious because they don’t. Thanks to the gospel-jazz core of their artistic personalities, their encompassing self-assurance in their craft’s portability of application, they make singing symbolic of existential struggle. It helps that they both love what Charlie Parker loved most about country music–storytelling.

Like Charles, Nelson absorbed the breadth of American music by living it. Born in poor Texas cotton country, Nelson and his sister Bobbie, who still plays piano for him, were raised by their grandparents, devout people and gospel-music fans who encouraged their grandchildren to pick up instruments. By the time the boy was 7 he was writing songs. “I was raised and worked in the cotton fields around Abbott,” he has said, “with a lot of African-Americans and a lot of Mexican-Americans, and we listened to their music all the time.” So blues and Mexican ballads underpin Nelson’s phrasing and narratives, along with the hillbilly and Western swing (13-year-old Willie once duetted with Western swing founder Bob Wills) that his radio picked up from Nashville and the border. Following a quick hitch in the Air Force and a tempestuous marriage to a Native American woman, Nelson moved in 1953 to Fort Worth, became a country deejay and played bars, mixing honky-tonk and preaching. (Nelson’s longtime drummer Paul English originally played with the Salvation Army.) In 1956 in Vancouver Nelson made his first record; it sold 3,000 copies. Then he wrote and sold a couple of hits, which got him a publishing contract and brought him to Nashville.

Producers there had little interest in demos of his nasal voice with its eccentric phrasing, and capitalized instead on Nelson’s songwriting. And yet now that those demos have surfaced on various reissues, they actually outline a central portion of Nelson’s work, since most made the Top 20 country charts, though almost always as performed by others. The low-key style of his bare-bones demos, however, grants Nelson’s lithe voice more space for embellishment, pauses and inflection than his released 1960s Nashville recordings, while showcasing his off-kilter lyrics, which refashion clichés from unexpected angles, on tunes like “Hello Walls” or “Crazy.” One outstanding example is “I Never Cared for You,” whose opening lines cleverly subvert Tin Pan Alley macrocosm/microcosm imagery: The sun never shines, the rain doesn’t fall and I never cared for you. In the liner notes to The Essential Willie Nelson, Emmylou Harris’s longtime collaborator, Rodney Crowell, recalls the song’s effect when he heard it over the radio in the mid-1960s: “A voice rivaling Bob Dylan’s in authenticity delivered the fantastically ironic lyric to a weird-sounding gut-string accompaniment.”

Ray Price was the first star to cover Nelson’s tunes; for a while Nelson played bass in Price’s band and wrote hits for Faron Young (“Hello Walls”), Billy Walker (“Funny How Time Slips Away”) and Patsy Cline (“Crazy”). But Nelson the singer suffered: His first label closed, and he kept being wedged into the curtain of syrupy strings that defined Nashville countrypolitan–a very 1950s sonic confection spun by producer Owen Bradley, modeled after the bland but influential approach to contemporary pop that Mitch Miller had fashioned as A&R head at Columbia. Countrypolitan gave the likes of Cline crossover appeal while trying to erase the singing rube/cowboy image that, via earlier movie and radio stars like Jimmie Rodgers and Gene Autry, first brought hillbilly music into mainstream markets. Nelson, who stubbornly resisted conforming, was a problem child.

He scored a couple of middling hits, but even though he joined the Grand Ole Opry and signed with RCA in 1965, he spent the next several years in limbo as a performer. The then-pudgy Nelson’s idiosyncratic, limber vocalizing and nonconformity, his insistence that his songs could sell themselves and his unwillingness to glitz up his act led to a constant, debilitating battle. Still, in the midst of a few blandly uneven countrypolitan discs, he managed to cut one of country music’s first concept albums, Yesterday’s Wine (RCA), a dazzling song cycle about a life from cradle to grave that demonstrated what he could do given his head.

By 1972 Nelson had quit Nashville and moved to Austin, where he noticed that young rock fans were turned on by honky-tonk and folk. (His way had been prepared, in part, by friend and colleague Johnny Cash’s eclectic 1970s TV show, showcasing the Man in Black, who had been performing at folk-music festivals for years, with folk-revival stars from Dylan to the Carter family.) Shrewdly, Nelson resurrected the country-folk-rock style that Nashville had rejected, enhanced by his lengthening hair, cowboy-Indian duds and hippie-crossover ideas. His old Music Row pals thought he’d killed what was left of his career. In fact, he had finally found his audience, post-1960s types who thought rock was too corporate and responded to Guthrie-esque storytelling minus the whiny self-indulgence of James Taylor, Carly Simon and Carole King–the same crowd Emmylou Harris would wow and Bruce Springsteen would tap with Nebraska and The Ghost of Tom Joad.

After an abortive stab at his own indie label, Nelson recorded with Atlantic, by then a major label that had mostly jettisoned r&b and jazz for the Rolling Stones and Led Zeppelin. With soul-music producer Arif Mardin and his own band (including pianist Leon Russell), Nelson cut killers like “Shotgun Willie,” which crossed funky soul back into country and rock, laced with the introspective touches and wry phrase-turnings that Nashville had scorned. In 1974, “Bloody Mary Morning,” a Texas-swing smoothie with characteristic witty lines (“It’s a bloody Mary morning baby left me without warning sometime in the night”), hit No. 14 on the country charts. At 41, Willie Nelson was finally hitting his stride.

One of my Austin-based colleagues comments with bemused affection, “Willie is the Buddha. He’s also a duet whore.” In terms of consistent quality, he’s right, but Nelson’s duets, which have included outings with Charles, Cash and Dylan as well as U2 and Julio Iglesias, if nothing else do reveal Nelson’s prismatic musical curiosity. Two classics (“Good Hearted Woman” and “Mammas Don’t Let Your Babies Grow Up to Be Cowboys”) boast Waylon Jennings, that other Outlaw who, with Nelson, launched the 1970s back-to-the-roots country movement, its revisionist rock, rockabilly and folk ingredients contrasting sharply with contemporary countrypolitan productions. Merle Haggard, another perpetual Nashville outsider, shows up for Townes Van Zandt’s evocative border ballad “Pancho and Lefty,” where Nelson’s nuance nicely plays off Haggard’s swagger while making clear that Haggard, whose band, the Strangers, routinely improvises, is among the few country singers whose jazzy phrasing–the dancing rhythms that infiltrated the best American singing after Louis Armstrong–compares to Nelson’s.

Red Headed Stranger (Columbia) in 1975 marked a pinnacle, Nelson’s John Wesley Harding, an artistic restatement of purpose in the guise of an Americana concept album about an Old West preacher who loved women; its brilliantly sparse, country-folk production features his voice and trademark nylon-stringed guitar. “Blue Eyes Crying in the Rain” shot to the top of the charts to make him a star. RCA, tailgating his success, compiled an album of Nelson, Jennings and others called Wanted! The Outlaws (RCA), the first country album to go platinum, thanks to “Good Hearted Woman.” A movement begun as a rejection of the Nashville music business became the business’s newest stack of chips in the hit-making casino.

Nelson hit No. 1 again with Lefty Frizzell’s sardonic “If You’ve Got the Money (I’ve Got the Time)” then cut a fine album of Frizzell tunes. When Bing Crosby died, to his label’s dismay Nelson abandoned what corporate types saw as a winning formula and zagged into the unsure turf of jazz-pop standards; he scored again: 1978’s Stardust (Columbia), arranged and produced by the MGs’ Booker T. Jones, triumphed with slow tempos and strings, as if Nelson had internalized Nashville and subtly refocused it. His jaunty phrasing genially enlivened classics like “Georgia on my Mind,” “Someone to Watch Over Me” and the title track. The album hung on the country charts for almost a decade.

Nelson never played it safe, as in career-building, and so success, like failure, didn’t stop his eclectic wanderings: a jam-based feel (Willie and Family Live, Columbia); covers of another renegade songwriter (Sings Kris Kristofferson, Columbia); pallid reprises of Stardust (Somewhere Over the Rainbow and Always on My Mind, both Columbia); reunions with Price (San Antonio Rose, Columbia) and Russell (One for the Road, Columbia). By 1985, however, old-timers like Nelson had begun to be swept away by New Country, the latest Nashville formula, brewed from reheated George Jones and Buck Owens. That year, Nelson founded Farm Aid, which lured performers like Dylan. Nelson also joined forces with Cash, Jennings and Kristofferson in The Highwaymen, a band of Nashville misfits who revivified the roots of country music and expanded the genre’s possibilities–and in the process extended its reach to the post-Eagles rock audience, eventually helping to make country music pop’s bestselling style with the widest radio play. In 1990 the IRS whacked Nelson for nearly $17 million in back taxes and seized practically all he owned. Who’ll Buy My Memories (Columbia), a twenty-five-cut compilation of Nelson-only demos, outtakes and keepers, was issued in 1992 to help pay off the debt; it remains one of Nelson’s most effective and affecting albums. The following year, he was solvent.

A collapsed lung, a pot bust, induction into the Country Music Hall of Fame, an ersatz acting career (The Electric Horseman, Thief, Wag the Dog, Austin Powers: The Spy Who Shagged Me)–Nelson is now legend enough to have songs written about him. Like Charles and Dylan, he’s grown so powerful and centered in his artistry that even his lesser efforts outgun the best of others.