McDonald and his band Country Joe and the Fish emerged from the Berkeley folk and psychedelic scene in the mid-1960s, blending acid rock with biting political commentary. The "Fish Cheer" — a call-and-response that spelled out an expletive before launching into the anti-war rag — became a rallying cry for a generation opposed to the Vietnam War.

His Woodstock performance, captured in the landmark 1970 documentary film, introduced the song to millions who had never attended a protest. The sardonic, darkly humorous lyrics — "And it's one, two, three, what are we fighting for?" — cut through the era's rhetoric with devastating simplicity.

McDonald continued performing and advocating for veterans' causes throughout his life, returning to the Woodstock site for the 40th anniversary concert in 2009.