Newport, R.I. ? It was a watershed event in popular music: Bob Dylan, folk music’s young minstrel, taking the stage with an electric guitar slung over his shoulder.

To the die-hard folkies at Newport on July 25, 1965, it was an outrage.

Bob Dylan in 1965

Thirty-seven years later, Dylan is coming back, headlining Saturday’s program at the Apple & Eve Newport Folk Festival.

His long-awaited return stirs memories of the day when he “plugged in,” was booed mercilessly and in the process knocked down barriers between folk and rock.

“There was an element of extreme Puritanism and tradition in the folk crowd, who really did feel that rock ‘n’ roll was just one big sellout,” says music historian Tim Riley, author of “Hard Rain: A Dylan Commentary.”

“It was like Dylan showed up at Newport and announced he was joining the other side.”

At 24, the skinny, wild-haired singer from Minnesota had been embraced as the spiritual and artistic leader of the American Folk Revival, which flourished on college campuses in the early ’60s and was championed by artists like Pete Seeger and Joan Baez.

Newport was the movement’s Mecca.

Rock was younger and dirtier. To folkies, the hip-swinging antics of Elvis Presley embodied rock ‘n’ roll. The televised swooning of Beatles fans didn’t help.

The 1965 festival was Dylan’s third appearance at Newport, and his Sunday afternoon set was the most anticipated of the weekend.

In April, he’d released “Bringing It all Back Home,” an album with six electric songs and six acoustic. Then, just four days before Newport, “Like a Rolling Stone” hit the airwaves.

Still, no one seemed prepared for Dylan to walk onstage toting a Fender guitar, accompanied by the Paul Butterfield Blues Band. They tore into a raucous version of “Maggie’s Farm,” and the crowd was stunned.

According to some accounts, Seeger had to be physically restrained from using an ax to cut the power cable. Dylan played just three songs and left the stage to an avalanche of catcalls.

A few minutes later, he returned, this time alone with an acoustic guitar and harmonica. He played two songs: “Mr. Tambourine Man,” and “It’s All Over Now, Baby Blue,” the latter a fitting requiem for his career as a folk singer.

Dylan, 61, has never spoken publicly about his reception at Newport.

For 37 years, he never came back to the festival. But when organizers announced he would be part of this year’s lineup, tickets sold out faster than in any year in recent memory.