Veteran rock musician Bob Weir, the Grateful Dead’s rhythm guitarist who helped guide the legendary jam band through decades of change and success, has died at age 78, according to a statement posted to his verified Instagram account on Friday.

He was diagnosed with cancer in July and “succumbed to underlying lung issues” surrounded by loved ones, the statement said. It did not mention when or where he died.

Along with his late fellow Grateful Dead co-founder and lead guitarist Jerry Garcia, who was at the center of the Deadhead universe, Weir was one of the group’s two frontmen and main vocalists for most of the band’s history.

It was Weir who sang the verses on the band’s trademark boogie anthem, Truckin’, and who wrote such key songs as Sugar Magnolia, Playing in the Band and Jack Straw.

The youthful, ponytailed “Bobby” grew into an eclectic songwriter whose handsome appearance and diverse musical influences helped broaden the band’s appeal. British newspaper the Independent called Weir “arguably rock’s greatest, if most eccentric, rhythm guitarist”.

After Garcia’s death at age 53 in 1995, Weir carved out an interesting if somewhat neglected solo career – much of it with his band, RatDog – and participated in reunions of surviving Dead members in different configurations.