Sam & Dave toured in the United States, Europe and Turkey, but their drug abuse had begun to take its toll. Their downward spiral was briefly slowed when John Belushi and Dan Aykroyd, as the Blues Brothers, recorded a hit version of “Soul Man” in late 1970s, bringing new attention to the original.

Sam Moore and Dave Prater performed together for the last time on New Year’s Eve 1981 in San Francisco. After walking offstage, they never spoke to each other again. Mr. Prater recruited a new partner, Sam Daniels, and they worked together, billed as Sam & Dave or the New Sam & Dave Revue — over Mr. Moore’s objections — until Mr. Prater died in a car accident in 1988.

Act III opened the year after that final show, when Mr. Moore married Joyce McRae, a self-described “upper-middle-class Jewish girl from Chicago” who had first seen him perform in 1967. She helped him get sober, took over managing his career and guided him through a productive professional twilight.

Sam & Dave were inducted into the Rock & Roll Hall of Fame in 1992 and received a lifetime achievement Grammy Award in 2019.

Mr. Moore’s solo album “Plenty Good Lovin’,” which he recorded in 1970 but Atlantic, for a variety of reasons, had declined to release, finally arrived to glowing reviews in 2002. He performed for presidents and recorded with Bruce Springsteen, Conway Twitty, Lou Reed and other singers. He also worked to help secure other performers’ and songwriters’ long-overdue copyrights and royalties.

A complete list of survivors was not immediately available.

“It’s been a roller-coaster ride, but mostly a good one,” Joyce Moore said in an interview in 2014. “The single most painful part has been realizing how abused and mistreated Sam and his peers were — and still are. Most of them have never gotten their due. But we’ve been blessed.”

Hank Sanders contributed reporting.