On a May night, backstage at Madison Square Garden, more than 50 musicians warmed up for a birthday party.
Folk hero Pete Seeger was turning 90, and the occasion brought out, in the words of the honoree, an "extraordinary guest list," including Dave Matthews and John Mellencamp.
"One of the first songs I would play on the guitar was a Pete Seeger song, 'If I Had a Hammer,'" Mellencamp said.
The celebration, which is being broadcast on PBS, reunited folk veterans like Joan Baez, Arlo Guthrie, Richie Havens, and Emmy Lou Harris.
"He's a living example of how … you can change the world one song at a time, one banjo tune at a time," Harris said.
In his 70-year career, Seeger had sung with many of them before, even the legendary Oscar the Grouch from "Sesame Street."
"Did you feel like you had to be here?" CBS News correspondent Anthony Mason asked the curmudgeonly Muppet for "CBS Sunday Morning."
"Oh, yeah, I had to be here. I wanted to wish him a rotten birthday!"
Less curmudgeonly was another guest singer named Bruce Springsteen, who described Seeger as "a walking repository of American music and conscience."
The only reluctant participant that night was the guest of honor himself.
"Do you like big birthday celebrations?" Mason asked.
"No," Seeger said.
"I don't like big things."
Pete Seeger, who always resisted celebrity, has become far bigger than he ever wanted to be.
Mason asked, "You don't like the word 'career,' do you?"
For Seeger, his life's work has been more of a mission, a musical evangelism, to rediscover and spread America's homegrown folk songs and entice even the most reluctant to sing along.
"Songs are sneaky things," Seeger once wrote. "They can slip across borders, penetrate hard shells."
He's given us some of his own songs, too: "If I Had a Hammer" . . . "Where Have All the Flowers Gone" . . . "Turn, Turn, Turn."
The son of musicians, Seeger hooked up with Woody Guthrie after dropping out of Harvard and headed cross-country hopping freight trains. It was Guthrie who taught him how to live off his music.
"He says, 'Pete, put your banjo on your back. Go in, buy a nickel beer and sip it slow as you can. Sooner or later somebody will say, 'Kid, I got a quarter for you if you pick us a tune.' Now, you swing around. Play your best song.' I managed to never go hungry."
On his banjo Seeger wrote "This machine surrounds hate and forces it to surrender" . . . an idea he got from Guthrie:
"He had a sign on his guitar saying, 'This machine kills fascists.' I wanted something a little more peaceful."
But he's carried that banjo into plenty of battles.
In the thirties, Seeger's social idealism had led him to join the Communist Party. Appearing at a labor rally in Peekskill, N.Y., in 1949 with black singer Paul Robeson, he faced a violent protest:
"There was a small crowd at the gate shouting, 'Go back to Russia.' 'Kikes.' 'Nigger lovers.'"
As Seeger drove away from the concert with his family, his car was battered with stones.
"It must have been terrifying," Mason said.
"Well, the family all went to the floor. And I held my head up as high as I could. And the glass flew around below me. But I kept on driving. I think in cases of danger I turn rather cold."
"Why is that?"
"I don't know."
A year later, Seeger would have his greatest commercial success with a quartet called The Weavers.
They recorded two songs, but it was the flip side that became the smash single. In 1950, "Goodnight Irene" spent 13 weeks at the top of the charts.
"I remember being in a restaurant. The jukebox was playing 'Goodnight Irene.' Somebody shouted, 'Turn that thing off. I've heard that song 50 times today!'"
But at the peak of their popularity, The Weavers became a prime target of the red scare:
"Well, the blacklisters must've said, 'How did we let commie so-and-sos slip through our fingers?' Right away they cut us down."
The group had agreed to do a weekly TV show on NBC; the sponsor was Van Kamp's Pork and Beans:
"But that very week, a little blacklisting magazine called Counterattack came out. And Van Camps never signed the contract."
In 1955, Seeger was subpoenaed to testify before the House Unamerican Activities Committee. Though he'd broken with the Communist Party, he invoked the First Amendment - the right of freedom of association - and refused to testify, saying: "I think these are very improper questions for any American to be asked."
He was convicted of contempt of Congress. But in 1962, the ruling was overturned.
How did he feel in the midst of being blacklisted?
"Oh, it was a joke," Seeger said. "The John Birch Society would try and stop me singing in some college. They'd get in the newspaper and said, 'This man is a goddamned Communist - don't go listen to him.' All they did was give me free publicity and sell more tickets."
His concerts at schools and colleges sowed the seeds for the folk revival of the early sixties.
And it was Seeger who introduced the Rev. Martin Luther King Jr. to an old folk song called "We Will Overcome," which he altered slightly.
"Why did you change 'will' to 'shall'?" Mason asked.
"Sings better," he said.
He has always practiced what he preached. It was Seeger's idea to build a replica sloop called the Clearwater to unite the community along New York's Hudson River to clean it up.
By his side, through it all, has been his wife Toshii, who as well as being the mother of their three children, has been his booker, publicity agent and accountant.
"She says, 'If Peter would only chase women instead of causes, I could leave him,'" Seeger said.
At 90, Seeger's voice has weakened, but he still loves to coax school-kids into a sing-a-long:
"What is it about singing for kids?" Mason asked.
"Oh, you can't look at those young faces without feeling there's some hope in the world."
And this past January, Pete Seeger, perhaps the most blacklisted artist in American history, was invited to perform for President Obama during the inauguration festivities in Washington.
"While taking some of his hardest knocks, he never lost," Springsteen said. "He just never lost his optimism. So it was an amazing thing to stand alongside of him that afternoon. Just to be there was an honor."
As Bruce Springsteen played with Seeger that day, he thought:
"'You outlasted 'em all, man! You know, you outlasted 'em all!' And something inside of him knew that that day, because he was so happy, he was so happy to be there."
For more info:
• "Great Performances: Pete Seeger's 90th Birthday Celebration from Madison Square Garden" (PBS)
• Clearwater (the environmental organization established by Seeger)
• "Pete Seeger Live in Australia 1963" (Acorn Media DVD)
• "Seeger at 89" (Amazon.com)
By CBS News correspondent Anthony Mason