Which single song by Johnny Cash became his first No. 1 hit on US 'Billboard' music charts?

"I Walk the Line" is a song written and recorded in 1956 by Johnny Cash. After three attempts with moderate chart ratings, it became Cash's first No. 1 hit on the US 'Billboard' Hot Country Songs chart, and eventually it reach No. 17 on the US 'Billboard' Hot 100 pop chart. The song which had been released by Sun Studio, Memphis, Tennessee remained on the record charts for over 43 weeks, and sold over two million copies.

When Cash wrote the song, he was 23 and married to his first wife, Vivian Liberto. Cash told his fans that he had been on tour and met temptation. He said the temptation is what led him to write "I Walk the Line". It is a proclamation of fidelity. "It was kind of a prodding to myself to, `Play it straight, Johnny'", Cash said.

The song is included in "The 500 Songs That Shaped Rock and Roll", and a permanent exhibit is located at the Rock and Roll Hall of Fame. In 2004, 'Rolling Stone' magazine ranked the song at No. 30 on its list of the 500 Greatest Songs of All Time. It was also ranked No. 1 on the list of the 100 greatest country songs of all time by 'Rolling Stone' in June 2014.