His mother, Frances Yauch, confirmed his death. He had been treated for cancer of the salivary gland for the last three years.
With a scratchy voice that grew scratchier through the years, Mr. Yauch rapped as MCA in the Beastie Boys, who were inducted into the Rock and Roll Hall of Fame this year. They offered many listeners in the 1980s their first exposure to hip-hop; they were vanguard white rappers who helped introduce the art of sampling and gained the respect of their African-American peers.
While many hip-hop careers are brief, the Beastie Boys appealed not only to the fans they reached in the 1980s but to successive generations, making million-selling albums into the 2000s, growing up without losing their sense of humor or their ear for a party beat.
Mr. Yauch (pronounced yowk) was a major factor in the Beastie Boys' evolution from their early incarnation, as testosterone-driven pranksters to their later years as sonic experimenters, as socially conscious rappers — championing the cause of freedom in Tibet — and as keepers of old-school hip-hop memories. The Beastie Boys became an institution — one that could have arisen only amid the artistic, social and accidental connections of New York City.
In the history of hip-hop, the Beastie Boys were both improbable and perhaps inevitable: appreciators, popularizers and extrapolators of a culture they weren't born into.
"The Beasties opened hip-hop music up to the suburbs," said Rick Rubin, who produced the group's 1986 debut album, in a recent interview with The Plain Dealer of Cleveland. "As crazy as they were, they seemed safe to Middle America, in a way black artists hadn't been up to that time."
The rapper Eminem said in a statement, "I think it's obvious to anyone how big of an influence the Beastie Boys were on me and so many others."
The Beastie Boys started their major-label career with two pivotal albums: "Licensed to Ill" (1986), a cornerstone of rap-rock that became the first hip-hop album to top the Billboard chart, and "Paul's Boutique" (1989), a wildly eclectic, sample-based production that became a template for experimental hip-hop.
The Beasties brand expanded well beyond music: with their own magazine and record label, Grand Royal; with the social activism of Mr. Yauch's Milarepa Foundation, which produced an international series of Tibetan Freedom Concerts; and with work in film, as Mr. Yauch (calling himself Nathanial Hörnblowér) directed Beastie Boys videos and went on , an independent film production and distribution company.
The Beastie Boys' appeal endured. Into the 2000s they could headline large events like the Coachella Valley Music and Arts Festival. Each of their albums up to "To the Five Boroughs" in 2004 has sold at least a million copies, and many of them have sold in the multimillions, in the United States alone.
"I burn the competition like a flame thrower/My rhymes they age like wine as I get older," Mr. Yauch rapped on the Beastie Boys' 2011 album, "Hot Sauce Committee Part Two."
When they started rapping in 1983, the Beastie Boys — Mr. Yauch, Adam Horovitz (Ad-Rock) and Mike Diamond (Mike D) — were greeted by some hip-hop purists as a novelty act. They were Jewish bohemians, not ghetto survivors; they were jokers, not battlers. Yet the Beastie Boys recorded for a label that was a bastion of New York hip-hop, Def Jam, and they toured alongside Run-D.M.C. and LL Cool J.
They went on to garner admiration and influence with productions that kept coming up with surprises — including, eventually, the rappers' playing instruments again — and with rhymes that would mingle humor, boasting and an increasing idealism. Even when the Beastie Boys were treated as a joke, it was a joke they would be in on for decades to come.
Adam Nathaniel Yauch was born on Aug. 5, 1964, in Brooklyn. Playing bass, he and Mr. Diamond started the Beastie Boys in 1981 as a hard-core punk band. The group's original drummer, Kate Schellenbach, has said, "Whereas other bands, just as awful as the Beastie Boys, would actually believe they were good, for Mike and Adam the whole point was to be terrible and admit it."
That group broke up after releasing an eight-song, seven-inch EP, "Polly Wog Stew." The Beastie Boys reappeared in 1983 with Mr. Horovitz on guitar, and made "Cooky Puss," a 12-inch single of prank phone call recordings over a rock guitar riff and hip-hop scratching. The group had been listening to New York hip-hop since the late 1970s.
