Possible Clues:

• 'Turn! Turn! Turn!' songwriter
• Grammy Lifetime Achievement Award recipient of '93
• "If I Had a Hammer" artist and activist
• "Turn! Turn! Turn!" folk singer
• Singer with the 1954 album 'Frontier Ballads'
• Musician called America's Tuning Fork
• Protest music pioneer
• He inspired a 2006 Springsteen album