Pete Seeger, who helped create the modern American folk music movement, co-wrote enduring songs such as If I Had a Hammer and in turn became a leading voice for social justice, has died at the age of 94.
He was variously hailed in social and traditional media as a "hero", "America's conscience" and "a man of the people".
Seeger died of natural causes at New York-Presbyterian Hospital, his record company, Appleseed Recordings, said.
Seeger was well known for his liberal politics, working as an environmentalist, protesting against wars from Vietnam to Iraq. He was sentenced to prison for refusing to testify to Congress about his time in the Communist Party.
In January 2009, Seeger performed at a concert marking Barack Obama's presidential inauguration.
He celebrated his 90th birthday in May of that year with a concert in New York's Madison Square Garden that drew 15,000 spectators and featured performers including Bruce Springsteen, John Mellencamp, Emmylou Harris, Arlo Guthrie, Joan Baez and Kris Kristofferson.
"Like a ripple that keeps going out from a pond, Mr Seeger's music will keep going out all over the world spreading the message of non-violence and peace and justice and equality for all," said Appleseed's Jim Musselman.
Seeger and Woody Guthrie started the Almanac Singers in the early 1940s, and nine years later Seeger became a founding member of another key folk group, the Weavers. Those groups opened the way for Bob Dylan and another generation of folk music singer/songwriters in the 1960s and 1970s.
The Weavers had a No 1 hit with a version of Lead Belly's Good Night, Irene and by 1952 had sold more than four million records. But the members drifted apart after being blacklisted for links to the Communist Party.
Seeger and Lee Hays wrote If I Had a Hammer for the Weavers, along with the hit So Long, It's Been Good to Know You.
Seeger also wrote the modern classic Turn! Turn! Turn! with lyrics from the Bible's book of Ecclesiastes and anti-war song Where Have All the Flowers Gone with Joe Hickerson.
But he was modest about his songwriting. "Hardly any of my songs have been written entirely by me," he once said. "I swiped things here and there and wrote new verses" to old tunes.
A key moment in New York-born Seeger's life was attending a mountain dance festival in North Carolina with his father.
"I lost my heart to the banjo," he said later. "It was an exciting sound and there was a kind of honesty in country music that I didn't find in pop music."
Seeger's career was derailed in 1951 when a book listed the Weavers as communists. During the next year, the group's record company dropped them and they were refused radio, television and concert appearances.
He refused to answer questions from the US House of Representatives Un-American Activities Committee in 1955, was prosecuted and sentenced to a year in jail in 1961. The conviction was overturned on appeal.
Despite his impact on American music, Seeger won just one Grammy for an album, 1997's Pete. He also received a Lifetime Achievement Grammy in 1993.
In 2007 Springsteen won the best traditional folk Grammy for We Shall Overcome - the Seeger Sessions, a collection of songs popularised by Seeger.