• He helped set up two major bands in the 1960s: The Byrds, and Crosby, Stills and Nash. He was renowned for his guitar-playing and vocal harmonies.
• His career saw him achieve the rare feat of being inducted to the revered Rock and Roll Hall of Fame twice.
Veteran US folk-rock star David Crosby has died aged 81, his representative has confirmed.
He helped set up two major bands in the 1960s: The Byrds, and Crosby, Stills and Nash. He was renowned for his guitar-playing and vocal harmonies.
His career saw him achieve the rare feat of being inducted to the revered Rock and Roll Hall of Fame twice.
Former bandmate Graham Nash expressed his "profound sadness", despite the two men's often "volatile" relationship.
Crosby's wife told showbiz site Variety that he died "after a long illness" while surrounded by family.
"His legacy will continue to live on through his legendary music," her statement added.
Crosby was born in California on 14 August 1941, the son of Oscar-winning Hollywood cinematographer Floyd Crosby.
He joined The Byrds in 1964 - a folk-rock group which scored its first hit with a cover of Bob Dylan's Tambourine Man.
His tempestuous tenure - a period during which he also briefly dated singer Joni Mitchell - culminated in his being fired from the group three years later.
Crosby, Stills and Nash came together as a supergroup soon afterwards, and performed at the legendary Woodstock festival in 1969.
They were later joined by Canadian singer-songwriter Neil Young. This band, too, was beset by in-fighting and broke up after a few years - though has periodically reformed for concerts since.
Hits written by Crosby during his time in the band included the hippy anthems Almost Cut My Hair and Deja Vu.
He became known for his countercultural politics and trademark moustache as well as his musicianship. A six-decade career culminated in his final album, For Free, released in 2021.
The record saw him team up with one of his children, James Raymond, who had been put up for adoption soon after birth and only became acquainted with his father three decades later.
Off-stage, Crosby had multiple run-ins with US law enforcement, including an arrest in 1982 on drug and weapons charges.
His substance abuse had reportedly intensified after the death of a girlfriend in a car crash when he was a young man.
There followed periods of ill health, and a liver transplant in 1994. Crosby's reputation for a hedonistic lifestyle saw him named two decades later as "rock's unlikeliest survivor" by Rolling Stone magazine.
Crosby later expressed regret over his addictions and altercations with co-stars, telling the Los Angeles Times in 2019 he was "ashamed" of some of his past behaviours.
Following the musician's death, Graham Nash wrote on social media that his late collaborator was "fearless in life and in music" and left behind a "tremendous void".
He acknowledged that they had a "volatile" relationship, but said "what has always mattered to David and me more than anything was the pure joy of the music we created together".
Another tribute came from Beach Boys singer Brian Wilson, who wrote on Twitter that he was "heartbroken" at the news - as his fellow star had been an "unbelievable talent" and a "wonderful person".
Tweets were sent from Crosby's own account the day before his death was announced - with one stating that Eleanor Rigby was his favourite Beatles to song to play on a rainy day.
The exact cause of his death was not immediately specified.