This episode aired on May 18, 2012.

Songs of social protest -- music and the quest for justice -- have long been intertwined, and the troubadours of troubling times -- Guthrie, Seeger, Baez, Dylan, and Springsteen among them -- have become famous for their dedication to both. Now we can add a name to the ranks of those who lift their voices for social and economic justice: Tom Morello.

Morello is the Harvard-educated guitarist who dabbled in politics, then chose rock music to make a difference. He played guitar for the popular band he co-founded -- Rage Against the Machine -- and then for Audioslave. Rolling Stone chose his album "World Wide Rebel Songs" as one of the best of 2011, and named him one of the 100 greatest guitarists of all time.

As likely to be spotted at a grass-roots rally as he would at a concert hall, Morello was in Madison, Wisconsin last year, braving bitter winter weather to sing on the steps of the state capitol in support of public service workers. Morello defended their collective bargaining rights against Republican Governor Scott Walker.

He was in New York City at the May Day demonstrations, an honorary commander of a battalion of musicians they called the "Occupy Guitarmy." That same night, Harry Belafonte presented Morello with the Officers' Award from the Sidney Hillman Foundation, honoring his "advocacy for and support of working people across the world."

Tom Morello shares his music, his message, and mission with Bill Moyers, who's all ears.