US singer and former Velvet Underground frontman Lou Reed has died at the age of 71.
Known for tracks including Perfect Day and Walk on the Wild Side, Reed was considered one of the most influential singers and songwriters in rock.
The Velvet Underground became renowned for their fusion of art and music and for collaborating with Andy Warhol.
According to the Associated Press news agency, Reed's literary agent said he died of a "liver-related ailment".
Andrew Wylie said the musician died at his home in Long Island, New York, on Sunday morning and had not been well "for a few months".
Reed's former Velvet Underground bandmate John Cale wrote on his website: "The world has lost a fine songwriter and poet… I've lost my 'school-yard buddy.'"
An admitted hard drinker and drug user for many years, Reed had a liver transplant this May after suffering liver failure.
"I am a triumph of modern medicine," Reed posted on his website on 1 June.
The Velvet Underground never achieved commercial success during their 1960s existence, but their influence on music in later decades was widely recognised.
The punk, glam and alternative rock movements of the 1970s, '80s and '90s were all indebted to Reed, whose songs were covered by the likes of REM, David Bowie, Nirvana, Patti Smith and countless others.
Music producer Brian Eno once summed up their influence by saying: "The first Velvet Underground album only sold 10,000 copies, but everyone who bought it formed a band."
The group were inducted into the Rock and Roll Hall of Fame in 1996.
After quitting The Velvet Underground in 1970, Reed released his self-titled debut in 1972, but it wasn't until the Bowie-produced LP Transformer later that year - which featured both Perfect Day and Walk on the Wild Side - that he achieved chart success.
Perfect Day enjoyed a second bout of success in 1996 when it was featured in Danny Boyle's Trainspotting, and again a year later when it was re-recorded by a celebrity cast for a BBC charity single.
As a solo artist, he released 20 studio albums. His last, Hudson River Wind Meditations, was released in 2007.
He is survived by his second wife, the musician and performing artist, Laurie Anderson.
Others paying tribute included US rock band Weezer, who said The Velvet Underground were "a big influence" when they were starting out.
Chic guitarist Nile Rogers said: "I did the Jools Holland show with him last year and we yucked it up. I didn't know he was ill."
Meanwhile, singer Marianne Faithfull said: "He was a great friend, musician, songwriter and band leader. One of the most intelligent musicians I've ever known and a great guitarist.
"His songs will live for ever... Perfect Day, Sweet Jane... In my opinion he was a genius. I will miss him terribly."
And Def Jam founder Russell Simmons tweeted: "New York lost one of our greatest gifts today."