Pete Seeger: Activist and humanitarian

Music legend Pete Seeger, who usually performed for the benefit of others, sings and plays banjo here during a concert marking his 90th birthday at Madison Square Garden in New York.  (Timothy A. Clary / AFP/Getty Images)

Seeger joins Willie Nelson on stage at the Farm Aid 2013 concert at Saratoga Performing Arts Center in Saratoga Springs, N.Y.  (Hans Pennink / Associated Press)

Seeger, 92, marches with nearly a thousand demonstrators sympathetic to the Occupy Wall Street protests for a brief acoustic concert in Columbus Circle in New York.  (John Minchillo / Associated Press)

Seeger, left, performs at the Rally for Détente at Carnegie Hall in New York. The rally sought a thawing of relations with the Soviet Union.  (Richard Drew / Associated Press)

Actor Kirk Douglas, left, director Harold Prince, singer Aretha Franklin, composer Morton Gould and singer Pete Seeger gather after a dinner in Washington, D.C., that honored them as recipients of the Kennedy Center Honors.  (Doug Mills / Associated Press)

Seeger, at age 81, speaks to students and faculty during a forum at Brandeis University in Waltham, Mass., called “Cultural Work, Coexistence and Community Development: A Conversation With Pete Seeger.”  (Steven Senne / Associated Press)

In Beacon, N.Y., Seeger leads a singalong while campaigning for the cleanup of the Hudson River.  (Time Roske / Associated Press)