Jerry Lawson, who for four decades was the lead singer of the eclectic cult-favorite a cappella group the Persuasions, has died. He was 75.

Lawson died Wednesday at a Phoenix hospice after a long illness, longtime friend and sometime Persuasions producer Rip Rense said.

Lawson’s smooth baritone led the group of five and later six singers, who were revered as the “The Kings of a Cappella” by their small but devoted fan base.

Through 25 albums the Persuasions recorded rock, blues, gospel and pop songs, all with no sound other than their own voices, long after the doo-wop era and long before the Pitch Perfect movies, when a cappella was rare.

“Thirty-eight years and we still ain’t got no band, man!” Lawson told The Associated Press in 2000. “That’s the story right there.”

They had many famous fans including Rod Stewart, the Grateful Dead’s Jerry Garcia, the members of Boyz II Men and Frank Zappa, who gave their career a boost when he discovered them in the late 1960s.

“After working together at the Hurricane Katrina Benefit Concert, I admired the undeniable depth in Jerry’s big voice,” Stewart said in a statement. “A true soul singer.”

They began as a casual and nameless collection of singers on the basketball courts and front stoops of Brooklyn in 1962, with Lawson bringing the warm, friendly voice he developed singing gospel songs during his youth in Apopka, Florida.

“It was just five guys who used to stand on the corner or go down to the subway station every night and just do this,” Persuasions member Jimmy Hayes told the AP in 2000.

Joseph Russell, Herbert Rhoad and Jayotis Washington rounded out the original quintet.

They got their break when Zappa signed them to his independent label for their first album in 1969.

The Persuasions performed with everyone from Liza Minnelli to Joni Mitchell to the Seattle Symphony Orchestra and covered the songs of Motown, Sam Cooke and Paul Simon.

The eclecticism that made them so beloved also kept them from reaching pop stardom.

Music executives never knew how to market them and commercial radio had no clue what niche to stick them in.

“They’ve never gotten their due,” Rense told the AP in 2000. “They’re the greatest, most enduring American a cappella group. In another country like Japan they’d be declared a living treasure.”

Lawson left the group in 2002. A few years later he joined a much younger group of San Francisco acapella singers that had based themselves on the Persuasions to form Jerry Lawson And The Talk of the Town.

The group released an album, co-produced by Lawson and his wife, in 2007, and in 2011 they appeared on NBC’s music competition show, The Sing-Off.

In 2015, he released his only solo album, Just a Mortal Man. The Persuasions were sampled on Jamie xx’s 2015 track “I Know There’s Gonna Be (Good Times).

A documentary on Lawson is in the works and is expected to be released later this year.

He is survived by wife Julie Lawson and daughters Yvette and Wanda Dawson.

At his request, no funeral will be held, his family said in a statement.