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 at age 78. Weir's death was announced Saturday in a statement on his Instagram page, per the AP. "It is with profound sadness that we share the passing of Bobby Weir," the statement said. "He transitioned peacefully, surrounded by loved ones, after courageously beating cancer as only Bobby could. Unfortunately, he succumbed to underlying lung issues."