David Crosby, from the Byrds and Crosby, Stills and Nash, dies ...

Singer-songwriter David Crosby, a founding member of 1960s folk-rock bands the Byrds and Crosby, Stills and Nash (CSN), has died aged 81.

His wife, Jan Dance, told Variety he died "after a long illness" while surrounded by family.

"His legacy will continue to live on through his legendary music," she said.  

Crosby was one of the most influential rock singers of the 1960s and '70s — including playing at Woodstock with Crosby, Stills, Nash and Young (CSNY) in 1969 — but was also a polarising figure.

His time in the spotlight was marked by a combative relationship with his band mates and a voracious drug habit that landed him in prison.

Crosby's UK-based representatives could not immediately be reached for comment by Reuters.

Despite his illness, Crosby's sense of humour and vocal activism persisted in recent days, with him tweeting support for Swedish environmentalist Greta Thunberg, and also describing heaven as "overrated … cloudy".

Crosby was a founding member of two revered rock bands: the country and folk-influenced Byrds, for whom he co-wrote the hit Eight Miles High, and CSNY, who defined the smooth side of the Woodstock generation's music.

He was inducted into the Rock & Roll Hall of Fame as a member of both groups.

Musically, Crosby stood out for his intricate vocal harmonies, unorthodox open tunings on guitar and incisive songwriting.

His work with both the Byrds and CSN/CSNY blended rock and folk in new ways and their music became a part of the soundtrack for the hippie era.

Personally, Crosby was the embodiment of the credo "sex, drugs and rock 'n' roll," and a 2014 Rolling Stone magazine article tagged him "rock's unlikeliest survivor".

In addition to drug addictions that ultimately led to a transplant to replace a liver worn out by decades of excess, his tumultuous life included a serious motorcycle accident, the death of a girlfriend, and battles against hepatitis C and diabetes.

"I'm concerned that the time I've got here is so short, and I'm pissed at myself, deeply, for the 10 years — at least — of time that I wasted just getting smashed," Crosby told the Los Angeles Times in July 2019.

"I'm ashamed of that."

He fell "as low as a human being can go", Crosby told the Times.

He also managed to alienate many of his famous former band mates, for which he often expressed remorse in recent years.

His drug habits and often-abrasive personality contributed to the demise of CSNY and the members eventually stopped speaking to each other.

In the 2019 documentary David Crosby: Remember My Name, he made clear he hoped they could work together again but conceded the others "really dislike me, strongly".

Crosby fathered six children — two as a sperm donor to rocker Melissa Etheridge's partner and another who was placed for adoption at birth and did not meet Crosby until he was in his 30s.

That son, James Raymond, would eventually become his musical collaborator.

Etheridge was among musicians taking to social media to pay tribute in the wake of his death.

Looking back at the turbulent 1960s and his life, Crosby told Time magazine in 2006: "We were right about civil rights; we were right about human rights; we were right about peace being better than war … But I think we didn't know our butt from a hole in the ground about drugs and that bit us pretty hard."

Crosby was born on August 14, 1941, in Los Angeles.

His father was a cinematographer who won a Golden Globe for High Noon in 1952 and his mother exposed him to the folk group the Weavers and to classical music.