Grateful Dead Founding Member Bob Weir Dead at 78

Bob Weir -- the guitarist and founding member of the Grateful Dead -- has died ... according to a statement posted to his official Instagram account.

According to the post ... Weir passed away while surrounded by loved ones due to an underlying lung issue after he beat cancer.

Weir was apparently diagnosed with cancer over the summer shortly before performing at Golden Gate Park in San Francisco for three shows celebrating the Grateful Dead's 60th anniversary.

The family goes on to say Bob often spoke of the Grateful Dead's lasting legacy ... adding he imagined the songs would live on for hundreds of years.

They write, "May that dream live on through future generations of Dead Heads. And so we send him off the way he sent so many of us on our way: with a farewell that isn’t an ending, but a blessing. A reward for a life worth livin’."

When Weir was just 16 years old, he famously followed the sounds of a banjo into a Palo Alto, California music store where he found Jerry Garcia strumming the instrument.

The two played music together all night ... and eventually decided to form the group which would later be known as the Grateful Dead. They -- along with Ron "Pigpen" McKernan, Phil Lesh and Bill Kreutzmann -- were the founding five members of the group.

Weir spent the next three decades -- besides a brief period in late 1968 when he and McKernan were left off the band's roster -- playing rhythm guitar and occasionally singing songs for the Dead.

During his time in the band, the group released 13 studio albums, many singles and played sold-out shows all over the world widely attended by their devoted fanbase the "Deadheads."

The Grateful Dead officially came to an end in 1995 after Garcia's death ... though Weir played with The Other Ones and The Dead -- successive groups made up of Grateful Dead members -- over the next two decades. Weir was inducted into the Rock & Roll Hall of Fame as a member of the Grateful Dead in 1994.

Weir also struck out on his own by founding the music group Bobby Weir & Wolf Bros in 2018 ... famously playing a series of shows with symphony orchestras at the Kennedy Center in 2022.

Like many members of the Grateful Dead, Weir also cared about social issues -- he was a longtime vegetarian and animal rights activist.

Weir is survived by his wife Natascha Münter and their two children, Monet and Chloe, who are asking for privacy at this time.

Bob was 78.