Beastie Boys rapper Adam Yauch has died at the age of 47, his publicist has confirmed to the BBC.
The musician, director and Tibet activist was diagnosed with salivary gland cancer in 2009.
Yauch underwent surgery and radiation therapy but said in 2011 reports he was totally cancer-free were "exaggerated".
Under the alias MCA, he formed part of the band that eventually became the Beastie Boys, selling 40 million albums worldwide with Mike D and Ad Roc.
Tributes have already been paid to the star on Twitter, with the likes of De La Soul, Ice T, Joe Satriani and Common passing on their condolences.
Rapper Biz Markie, who collaborated with the Beastie Boys on their Ill Communication album, wrote: "My brother, you are truly going to be missed. My heart is heavy."
Fellow New Yorker Moby added: "I'm very, very sad to hear of Adam Yauch's passing. He was a wonderful, generous, remarkable, and inspiring man and friend."
In a nod to the scope of the group's fame, New York Senator Chuck Schumer also tweeted his condolences: "Born and Bred in Brooklyn, U.S.A., they call him Adam Yauch, but he's M.C.A. RIP Adam."
Justin Timberlake said he was "crushed" by the news, while Nirvana's bassist Krist Novoselic thanked Yauch for his "Sabotage bass riff and many other great grooves".
The Beastie Boys started out as a hardcore punk outfit called The Young Aborigines in 1979 but switched to hip hop in 1984.
Two years later they launched their critically-acclaimed debut album Licensed To Ill, which spawned the hit singles (You Gotta) Fight For Your Right (To Party) and No Sleep Till Brooklyn.
Fusing rock guitars with lo-fi hip-hop beats, Licensed To Ill was one of the first rap records to cross over to a mainstream audience - and the first to top the US charts.
But the band became equally well-known for their bratty, bad-boy personas.
They were lambasted in the British press for their stage show, which featured giant inflatable phalluses and cage dancers.
And, when they began to wear the Volkswagen emblem on chains around their necks, it reportedly led to a rise in vandalised cars.
Their obnoxious behaviour undoubtedly started as an in-joke but became something of a self-fulfilling prophecy as their fame increased.
Over the years, however, the Beastie Boys rehabilitated their image.
Their second album, Paul's Boutique, was retrospectively considered a masterpiece, its genre-bending sound collages paving the way for the likes of Beck and The Avalanches.
Later records saw them play their own instruments and expand their horizons beyond hip-hop.
In 1996, they released The In Sound From Way Out! - a collection of jazz and funk instrumentals, while the group collaborated with reggae legend Lee "Scratch" Perry on 1998's Hello Nasty.
But they are best remembered for their hardcore rap tracks - Sure Shot, Sabotage and the crossover hit Intergalactic.
Yauch was the band's filmographer, directing several of their videos under the pseudonym Nathaniel Hornblower.
He also directed the band's concert movie Awesome... I Shot That, which stitched together footage from dozens of audience-members.
The rapper grew up in Brooklyn, and was fascinated by electronics and explosives at a young age, building small home-made bombs from fireworks he had hoarded at home.
Aged 14, he removed himself from a Quaker school to join a public high school in New York. "I felt I was leading too much of a sheltered life," he told Rolling Stone in 1998.
There he taught himself bass guitar, after discovering punk through The Clash's debut album.
His new schoolfriends also introduced him to his future bandmates for the first time.
In addition to his rap career, Yauch was heavily involved in the Free Tibet movement, and co-organised several fundraising concerts in the 1990s.
"I think that movies and CDs... they affect the way people think," he told PBS in 1997. "I know they've radically affected the way I think."
He revealed he had cancer in a salivary gland in his neck in July 2009, which led to the scrapping of a tour and an album - Hot Sauce Committee, Pt 1.
In an email to fans later that year, he said the tumour had been removed and he was feeling "healthy, strong and hopeful".
Yauch travelled to a Tibetan community in Dharamsala in India after surgery.
He told fans: "I'm taking Tibetan medicine and at the recommendation of the Tibetan doctors I've been eating a vegan/organic diet."
But in January 2010, he was forced to deny press reports that he was fully recovered.
"I'm continuing treatment, staying optimistic and hoping to be cancer free in the near future," he said in a statement.
The Beastie Boys were inducted into the Rock and Roll Hall of Fame last month, but Yauch was not able to attend. On the night, The Red Hot Chili Peppers dedicated their performance to Yauch.
He is survived by his wife, Dechen Wangdu, and their daughter, Tenzin Losel, as well as his parents Frances and Noel Yauch.