Brenner was born into an Orthodox Jewish family. He developed an interest in history from reading Hendrik Willem van Loon's The Story of Mankind which his brother had received as a bar mitzvah present. He became an atheist at age 10 or 12 and a Marxist at age 15. Brenner's involvement with the Civil Rights Movement began when he met James Farmer of the Congress of Racial Equality, later the organizer of the Freedom Rides of the early 1960s. He also worked with Bayard Rustin, later the organizer of Martin Luther King's 1963 "I Have a Dream" march on Washington.
Brenner was arrested three times during civil rights sit-ins in the San Francisco Bay Area. He spent 39 months in jail when a court revoked his probation for marijuana possession, because of his activities during the Berkeley Free Speech Movement at the University of California in 1964.
He was an anti-war activist from the first days of the Vietnam War, speaking frequently at rallies in the Bay Area. In 1963 he organized the Committee for Narcotic Reform in Berkeley. In 1968 he co-founded the National Association for Irish Justice, the American affiliate of the Northern Ireland Civil Rights Association.
(Taken from Wikipedia)