Cash was known for his deep, calm bass-baritone voice, the distinctive sound of his Tennessee Three backing band, a rebelliousness coupled with an increasingly somber and humble demeanor, free prison concerts, and a trademark look, which earned him the nickname "The Man in Black". He traditionally began his concerts with the simple "Hello, I'm Johnny Cash", followed by his signature "Folsom Prison Blues".
Much of Cash's music echoed themes of sorrow, moral tribulation and redemption, especially in the later stages of his career. His best-known songs included "I Walk the Line", "Folsom Prison Blues", "Ring of Fire", "Get Rhythm" and "Man in Black". He also recorded humorous numbers like "One Piece at a Time" and "A Boy Named Sue"; a duet with his future wife, June Carter, called "Jackson" (followed by many further duets after their marriage); and railroad songs including "Hey, Porter" and "Rock Island Line". During the last stage of his career, Cash covered songs by several late 20th century rock artists, most notably "Hurt" by Nine Inch Nails.