Later this year, Rick Rubin’s American Recordings label will release a collection of Johnny Cash songs including a collaboration between the legendary country singer and one of his greatest fans, the Clash’s Joe Strummer. The pair’s version of Bob Marley’s “Redemption Song” will serve as a poignant reminder of why Cash, who died Friday at age 71, was so revered by his fellow musicians — if not always by a music industry that had a hard time figuring him out.

“In a garden full of weeds,” explained U2’s Bono, Cash was “the oak tree.”

Cash loved playing with younger artists who shared his recognition that a song ought to come with an edge — and maybe even a little politics. His collaborations with Bob Dylan, U2 and Strummer, and the delight with which he covered songs by Nine Inch Nails, Nick Cave, Beck, Tom Waits and Bruce Springsteen, made it impossible to slot Cash into the narrow categories where contemporary radio programmers consign artists. “He’s an outsider, never been part of a trend,” Rubin said of Cash.

In his remarkable 1997 autobiography, Cash reflected on a career that began with hit singles but eventually saw him searching for a proper record label — a search that ended only when Rubin, a groundbreaking rock and rap producer, signed him to American Recordings and produced four starkly brilliant albums. When people wondered why a country singer was on his label, Rubin said, “A rock star is a musical outlaw and that’s Johnny.”

Cash embraced that outlaw image, singing in his signature song, “Man in Black”:

“Well you wonder why I always dress in black/Why you never see bright colors on my back/And why does my appearance seem to have a somber tone/Well there’s a reason for the things that I have on/I wear the black for the poor and the beaten down/Livin’ 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 times.”

Later in the song, he referenced the war in Vietnam, singing: “I wear the black in mourning for the lives that could have been/Each week we lose a hundred fine young men.”

Cash took sides in his own songs, and in the songs he chose to sing. And he preferred the side of those imprisoned by the law — and by economics. Cash’s obituaries are quick to quote the lines at the start of his classic song, “Folsom Prison Blues,” which go:

When I was just a baby my mama told me son/Always be a good boy don’t ever play with guns/But I shot a man in Reno just to watch him die…

Later in the song about a prisoner listening to a passing train, however, Cash sings:

I bet there’s rich folks eatin’ in some fancy dining car/They’re probably drinkin’ coffee and smokin’ big cigars/Well I know I had it comin’ I know I can’t be free/But those people keep a movin’ and that’s what tortures me

Though he was not known as an expressly political artist, Cash waded into the controversies of his times with a passion. Like the US troops in Vietnam who idolized him, he questioned the wisdom of that war. And in the mid-1960s, at the height of his success, he released an album that challenged his country’s treatment of Native Americans. That album, Bitter Tears, featured an powerful version of Peter LaFarge’s “As Long as the Grass Shall Grow,” a sad, angry rumination on the mistreatment of the Seneca tribe of the Iroquois nation, and of how the US government “broke the ancient treaty with a politician’s grin.”

Years later, Cash would remember that, as he prepared Bitter Tears, “I dove into primary and secondary sources, immersing myself in the tragic stories of the Cherokee and the Apache, among others, until I was almost as raw as Peter. By the time I actually recorded the album I carried a heavy load of sadness and outrage; I felt every word of those songs, particularly ‘Apache Tears’ and ‘The Ballad of Ira Hayes.’ I meant every word, too. I was long past pulling my punches.”

The Bitter Tears project inspired one of Cash’s many disputes with a music industry that wanted him to entertain rather than educate.

“I expected there to be trouble with that album, and there was,” Cash wrote in his autobiography. “I got a lot of flak from the Columbia Records bosses while I was recording it — though Frank Jones, my producer, had the sense and courage to let me go ahead and do what I wanted — and when it was released, many radio stations wouldn’t play it. My reaction was to write the disc jockeys a letter and pay to have it published as a full-page ad in Billboard. It talked about them wanting to ‘wallow in meaninglessness’ and noted their ‘lack of vision for our music.’ Predictably enough, it got me off the air in more places than it got me on.”

Even in the 1960s, Cash said, “craven worship of the almighty dollar” was interfering with the ability of artists to get good music heard.

Thirty years later, as Clear Channel and other radio conglomerates sucked what life there was out of radio, Cash would argue, “The very idea of unconventional or even original ideas ending up on ‘country’ radio in the late 1990s is absurd.”

In 1998, after Cash won the Grammy award for best country album, American Recordings purchased a full-page ad in Billboard that was addressed to country radio programmers who had failed to play his music. The ad featured a picture of a much younger Cash with his middle finger held high in a fierce gesture of defiance.

Even as Cash was widely honored in his last years, his music was seldom played on mainstream country radio. And, yet, Johnny Cash kept being heard, singing the last track of a U2 album, appearing in a haunting video that somehow found a place on MTV and joining in that one last “Redemption Song” with a late British punk named Strummer who recognized that no one rocked like the Man in Black.