John R. "Johnny" Cash was a singer-songwriter, actor, and author, widely considered one of the most influential American musicians of the 20th century. Although primarily remembered as a country icon, his genre-spanning songs and sound embraced rock and roll, rockabilly, blues, folk, and gospel. This crossover appeal won Cash the rare honor of multiple induction in the Country Music, Rock and Roll, and Gospel Music Halls of Fame. Cash was known for his deep bass-baritone voice, distinctive sound of his Tennessee Three backing band, a rebelliousness coupled with an increasingly somber and humble demeanor, free prison concerts, and 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"; 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.