LOS ANGELES (AP) — Phil Lesh, a classically trained violinist and jazz trumpeter who found his true calling reinventing the role of rock bass guitar as a founding member of the Grateful Dead, died Friday at age 84.

Lesh’s death was announced on his Instagram account. Lesh was the oldest and one of the longest surviving members of the band that came to define the acid rock sound emanating from San Francisco in the 1960s.

“Phil Lesh, bassist and founding member of The Grateful Dead, passed peacefully this morning. He was surrounded by his family and full of love. Phil brought immense joy to everyone around him and leaves behind a legacy of music and love,” the Instagram statement reads in part.

The statement did not cite a specific cause of death and attempts to reach representatives for additional details were not immediately successful. Lesh had previously survived bouts of prostate cancer, bladder cancer and a 1998 liver transplant necessitated by the debilitating effects of a hepatitis C infection and years of heavy drinking.

Although he kept a relatively low public profile, rarely granting interviews or speaking to the audience, fans and fellow band members recognized Lesh as a critical member of the Grateful Dead whose thundering lines on the six-string electric bass provided a brilliant counterpoint to lead guitarist Jerry Garcia’s soaring solos and anchored the band’s famous marathon jams.

“When Phil’s happening the band’s happening,” Garcia once said.

Drummer Mickey Hart called him the group’s intellectual who brought a classical composer’s mind-set and skills to a five-chord rock ‘n’ roll band.