Dennis Banks, who helped found the American Indian Movement and engaged in sometimes-violent uprisings against the U.S. government, including the armed occupation of Wounded Knee in 1973, died at age 80, his family announced Monday.

Banks, whose Ojibwe name was Nowacumig, was one of several activists who founded AIM in Minneapolis in 1968, and he was a leader of the group’s takeover of Wounded Knee on the Pine Ridge Reservation in South Dakota in 1973, in a protest against both the U.S. and tribal governments. The village had been the site of a massacre by U.S. soldiers in 1890 that left an estimated 300 Indians dead. The occupiers held federal agents at bay for 71 days; two Native Americans died and several agents were injured amid the frequent gunfire.