LOS ANGELES — Bob Weir, the guitarist and singer who as an essential member of the Grateful Dead helped found the sound of the San Francisco counterculture of the 1960s and kept it alive through decades of endless tours and marathon jams, has died. He was 78.

Weir’s death was announced Saturday in a statement on his Instagram page.

“It is with profound sadness that we share the passing of Bobby Weir,” a statement on his Instagram posted Saturday said. “He transitioned peacefully, surrounded by loved ones, after courageously beating cancer as only Bobby could. Unfortunately, he succumbed to underlying lung issues.”

The statement did not say where or when Weir died, but he lived in the San Francisco Bay Area for most of his life.

Weir joined the Grateful Dead — originally the Warlocks — in 1965 in San Francisco at just 17 years old. He would spend the next 30 years playing on endless tours with the Grateful Dead alongside fellow singer and guitarist Jerry Garcia, who died in 1995.

Weir wrote or co-wrote and sang lead vocals on Dead classics including “Sugar Magnolia,” “One More Saturday Night” and “Mexicali Blues.”

After Garcia’s death, he would be the Dead’s most recognizable face. In the decades since, he kept playing with other projects that kept alive the band’s music and legendary fan base, including Dead & Company.