Zellner was involved in numerous civil rights efforts, including nonviolence workshops at Talladega College, protests for integration in Danville, Virginia, and organizing Freedom Schools in Greenwood, Mississippi, in 1964.

He later taught the history of the civil rights movement at Long Island University and published a memoir of his activism that was adapted into the 2020 film Son of the South, with Lucas Till portraying him.

[1][2][a] He was named after his godfather and the officiant at his parents' wedding, Bob Jones Sr.[5] His relatives were involved in the Ku Klux Klan (KKK) and his father and grandfather were members.

[6] Zellner's father organized for the white supremacist group but eventually left the Klan after supporting Jewish resistance in German-occupied Europe during World War II.

He responded by suggesting they visit the library or conduct field research through the KKK or white citizens' council, and told the five it "won't be necessary" to study multiple points of view in the issue of race.

[8] The five disregarded his instructions and discussed civil rights with students at the Alabama State College for Negroes and visited the MIA's offices.

[8][6] The group ended up interviewing King, Rosa Parks, and E. D. Nixon, catalyzing Zellner's interest in the civil rights movement.

[7][9] The white community did not approve, and Zellner had crosses burned outside his dorm by the KKK, the school suggested his expulsion, and the Attorney General of Alabama accused him of communism.

[1][2] As a civil rights activist, Zellner was beaten unconscious several times, leading to brain damage and post-traumatic stress disorder.

He was severely beaten by white men after protesting the murder of Herbert Lee, as well as the expulsion of Brenda Travis and Ike Lewis from Burglund High School.

[19] He continued his project without their support, moving with his wife, Dorothy Zellner, to the Gulf Coast and establishing the Grass-Roots Organizing Workers (GROW; also known as Get Rid of [George] Wallace).

[6] An oral history based on interviews with Zellner is included in the 2006 book Generation on Fire: Voices of Protest from the 1960s by Jeff Kisseloff.