Folk-Rock Voice of the 1960s Whose Influence Spanned Decades, Dies at 81

He was an original member of the Byrds and a founder of Crosby, Stills & Nash. But he was almost as well known for his troubled personal life as for his music.

David Crosby, the outspoken and often troubled singer, songwriter and guitarist who helped create two of the most influential and beloved American bands of the classic-rock era of the 1960s and ’70s, the Byrds and Crosby, Stills, Nash & Young, has died. He was 81.

Patricia Dance, a sister of Mr. Crosby’s wife, Jan Dance, said in a text message on Thursday evening that Mr. Crosby died “last night.” She provided no other details.

Mr. Crosby was inducted twice into the Rock & Roll Hall of Fame, as a founding member of the Byrds and as a founder of Crosby, Stills & Nash. He brought jazz influences to both groups, in the process broadening the possibilities of vocally driven folk-rock. And his reach extended to later generations: His alternate tunings became an inspiration for the innovative “freak folk” movement of the early 21st century while influencing scores of other musicians eager to give acoustic music a progressive spin.

He was an original member of the Byrds and a founder of Crosby, Stills & Nash. But he was almost as well known for his troubled personal life as for his music.