Mark Volman, co-founder of the 1960s rock band The Turtles, has died at the age of 78.

He passed away on September 5 in Nashville, Tennessee, after a brief and unexpected illness, according to his representative per PEOPLE.

Volman and his band rose to fame 60 years ago with their hit version of Bob Dylan’s It Ain’t Me Babe, which became their first Top 10 single in 1965.

Mark Volman, born on April 19, 1947, in Los Angeles, California, was a founding member of the influential 1960s rock band The Turtles. Alongside Howard Kaylan, he created one of the era’s most distinctive pop sounds, blending folk-rock with harmonies that helped the group score major hits. Their breakout came in 1965 with a cover of Bob Dylan’s It Ain’t Me Babe, followed by enduring classics like Happy Together and She’d Rather Be With Me.

When The Turtles disbanded in 1970, Volman and Kaylan continued performing together as Flo & Eddie, joining Frank Zappa’s Mothers of Invention before launching their own act. Known for their humor and strong vocal blend, the duo built a loyal following and contributed backing vocals to many major artists, including T. Rex, Alice Cooper, and Bruce Springsteen.

In addition to performing, Volman built a career as a music industry educator. After earning a college degree later in life, he taught music business and communications at institutions such as Belmont University in Nashville.

Beyond music, Volman was admired for his resilience. He survived health struggles, including a cancer diagnosis in 2015, and remained active in music and teaching for some years afterward.

In 2020, Volman was diagnosed with Lewy body dementia, a condition that affects memory, movement, and thinking. It is the second most common form of dementia after Alzheimer’s disease. With the help of medication to manage tremors and hallucinations, he was still able to join the Happy Together tour, according to the New York Post.

The Turtles later reunited to headline the popular ’60s music festival. Volman carried the band forward on stage, as his longtime collaborator Howard Kaylan was unable to tour due to health challenges of his own.

In his 2023 memoir Happy Forever, Mark Volman looked back on his rock ‘n’ roll adventures, including wild nights spent with legends like Jimi Hendrix and John Lennon. Promoting the book, he told People that those times felt like a dream and admitted he always felt like “a groupie at heart.”