(CBS News) The professional highs and personal lows of Johnny Cash are highly documented, but a former music critic, Robert Hilburn, is revealing surprising new details about the legendary singer in his new book "Johnny Cash: The Life."
In 1956, "I Walk the Line" hit number one on the country charts. Johnny Cash was at the beginning of a career that soared and crashed more than once, a career nearly ruined by drug abuse.
After a high profile arrest on drug charges, Johnny Cash was trying to re-start his career with what would become a legendary concert at Folsom Prison in 1968.
"It was a very tense environment because two weeks before there had been a guard captured as a hostage," said Hilbrun. "And there were guys on this catwalk above the thing walking around with machine guns, so it was - I was a little nervous you know."
Hilburn was a young journalist at the show and was photographed standing next to Johnny Cash as he was about to take the stage.
"The moment that's chilling is, he's singing 'Folsom Prison Blues' and he gets to the line, 'I shot a man in Reno just to watch him die,'" said Hilburn. "Whoa - the audience screams!"
Johnny Cash never served prison time, although he did spend several nights in jail and cultivated his reputation as an outlaw. In his new biography, Hilburn wrote of the artistry and pain in Johnny Cash's life connected by a string of failed relationships.
"Roseanne Cash, his daughter, showed me letters that he wrote to her in the '70s, '80s and still in the '90s saying 'please forgive me, I still love you,'" said Hilburn. "He was always pleading for their love."
Roseanne Cash is one of four daughters Johnny Cash had with his first wife Vivian. The couple met just before he was sent off to Germany with the military.
"They know each other 17 days. He goes into the Air Force and they write each other for three years back and forth," said Hilburn. "He's thinking the whole time, 'I'm gonna come home, I'm gonna marry Vivian and I'm gonna go on the road and be gone 300 days a year singing my music.' She's thinking he's gonna come home, he's gonna marry me and he's going to stay with me. It's gonna be like 'Ozzie and Harriet.'"
It wasn't. Johnny Cash's music soon came between him and his family.
"So gradually he starts staying away from home more often. He starts feeling guilty about that. He starts taking pills, he learns he's addicted to pills," said Hilburn.
His affair and eventual marriage to June Carter forms the centerpiece of the 2005 Oscar winning movie, "Walk the Line."
Their relationship was even more unsettled than depicted in the film, according to Hilburn. So unsettled it inspired the song "Ring of Fire".
Hilburn told CBS News' John Blackstone that Johnny Cash did not actually write the iconic, "Ring of Fire."
"June Carter wrote it about their relationship - whoosh, it was a ring of fire - they were both married," said Hilburn. "They would both shout, 'You get divorced, no you get divorced.' They would break up, he would start dating other people, sometimes June's sister,"
Hilburn told Blackstone that first, June Carter wrote "Ring of Fire" and gave it to her sister Anita Carter to record, but no one bought the song until Johnny Cash recorded it.
"When he needs one hit record he goes back to that song and he bets his whole career on that song," he said.
Johnny Cash himself wrote more than 1,000 songs and had an I.Q. of 160. Yet, "Folsom Prison Blues" was inspired, to put it delicately, by a Gordon Jenkins song, "Crescent City Blues."
"Eighty percent of the song is the same, so his first hit was really quote 'lifted' let's say," said Hilburn. "I don't like to use the word stole, he changed it significantly, but yes, he stole it, he stole it."
Hilburn told Blackstone that Johnny Cash had a lot of regrets.
"Think about it: the children, the drugs - he regretted the way he kind of let his career slip away and he thought he lost his legacy until this final round of recordings," said Hilburn.
Those final recordings included "Hurt" from a hit by Nine Inch Nails. It was one of many late-in-life collaborations with producer Rick Rubin. Their last album released in 2003, the year Cash died, sold more than 2 million copies, renewing his legacy as an artist and a star.
"In the end it all came back. The children, he had their love. June and him could not have been better off. The fans came back. So on his deathbed, Johnny Cash who always said, 'you can be redeemed,' he was redeemed," said Hilburn.