In Hot Press magazine, The Edge wrote about Johnny Cash being punk:

I think it was his combining so many things that people were interested in, the political awareness and a sense of righteous anger of behalf of the downtrodden and the disenfranchised, whether they were the inmates of San Quentin or just the working class people that he knew so well in America and wrote so eloquently about. He always seemed to be up for the underdog and that just sat so well with what punk rock was all about.

He also talked about how it came to pass that Cash sang "The Wanderer" on U2's Zooropa:

"I think like so many of our best ideas, 'The Wanderer' happened almost by magic. We were working on the song, Bono got on the mic to sing and he was going, 'I dunno quite how I'm gonna approach this one.' And out of the blue he said, 'Hey, y'know, I think Johnny Cash is in town, maybe we could get him to come and sing on this, with me or instead of me.'