Dellinger was notable for being a pacifist and an advocate for nonviolent social change, to the point where he was imprisoned during World War II as a conscientious objector. He joined many social movements of the 1950s and '60s, including civil rights marches in the South. Later in life, he continued his activism, up until the very last few years before his death in 2004. In fact, in 1996, when the Democratic National Convention returned to Chicago for the first time, he was arrested again for a sit-in protest.