Johnny Cash. He was many things in life and remains many things in legacy. One of the most important figures in the history of country music; a devoutly religious rebel; a black-clad troubadour; a classical paradox of a man. Throughout his career, he was defined by songs that were, all at once, violent and mournful, steady in sound and chaotic in spirit.

Cash walked the line (pun intended) of a brilliant and tumultuous time for country music and for popular music in general – the line between standards and covers, between singers and songwriters and singer-songwriters; between rebellion and redemption. The very concept of covers emerged from the dawn of the singer-songwriters, the folks whose songs were first and foremost associated with them. Gone, in most arenas of popular music, were the songs that every artist would take on to earn their chops and pay their respects.

Country music was one of the few genres where standards held strong alongside original material and covers remained the norm, alongside blues and folk and other such tradition-based music. As the years pass, though, traditions change and musicians are faced with new challenges and questions. Does an artist keep on recording songs written by their contemporaries? Do they take on new music from musicians generations younger than them? Do they stick to the themes and styles that their reputations were built on in the first place? Many artists trembled at the challenge, many faltered; but Johnny Cash, with his American Recordings series, had one answer to all of these questions: yes.

Tom Petty and the Heartbreakers served as Cash’s backing band on Unchained (American II), and Petty had this to say (from an Uncut interview) of the eclecticism that came to define the American series:

It was incredible. He was an interesting artist because he’s pictured as a country artist, but he wasn’t necessarily completely in that bag, you know. I always thought of him as a folk artist. Because he knew so much about folk music. And the country that he performed wasn’t really much like any other country that you’d heard. It was an unusual thing, his bag was pretty wide.

Released over the course of just over fifteen years, including two albums released posthumously, the American series remains a landmark not only in Cash’s career and in the history of country music, but in all popular music. All at once, it was old and new, traditional and revolutionary.

For those who aren’t altogether familiar with Cash’s music (or at least his American-era music), the distinguishing track of the series would seem to be American IV’s cover of Nine Inch Nails’ “Hurt.” While there is an inescapable accuracy to the assessment, it’s a limiting view and one that could likely cause folks to miss out on the enormous variety of the series.

While “Hurt” isn’t representative of the entire series of albums, it does indeed serve as a mark of distinction. As a whole, the albums reflect on many themes – remorse and violent anger; hopelessness and hope; loss and love and longing; fear and faith. Between the canonical series and Unearthed‘s four discs of outtakes, Cash covered everything ranging from the Beatles to Bob Marley, from Simon and Garfunkel to Neil Young to Biblical hymns and timeless ballads. With the covers in the vein of “Hurt,” however, Cash attacks his classic themes in entirely new ways. He retains his distinctive sound, both vocally and instrumentally, but he lets that sound sink its teeth deep into a different kind of source material.

Cash treats the American series with something of a slow-burning approach. As it is, “Hurt” seems like a radical cover four albums into the series, but the progression to American IV and beyond it shows the greatness of Cash’s covers to be as much a matter of timing and context as anything else. This is not a statement to diminish the covers, but rather to diminish the distinction between a Cash cover and a Cash classic. There is none.

Cash’s takes on newer music (new being relative to the vast span of his career and to the genres he takes on), fitting and transformative as they may be, are not wholly representative of the American series. They capture an aspect of his work’s progression, his consistent ability to do new things after half a century of making music, but they are not alone in doing so. He approaches the work of his contemporaries and his more direct heirs with the same care and the same familiarity as he brings to the more dramatic changes.