Dennis J. Banks, the militant Chippewa who founded the American Indian Movement in 1968 and led often-violent insurrections to protest the treatment of Native Americans and the nation’s history of injustices against its indigenous peoples, died on Sunday night at the Mayo Clinic in Rochester, Minn. He was 80.

His daughter Tashina Banks Rama said the cause was complications of pneumonia following successful open-heart surgery a week ago at the clinic. Mr. Banks lived on the Leech Lake Reservation in northern Minnesota, where he was born and where he grew up.

Mr. Banks and his Oglala Sioux compatriot Russell Means were by the mid-1970s perhaps the nation’s best-known Native Americans since Sitting Bull and Crazy Horse, who led the attack that crushed the cavalry forces of Lt. Col. George Armstrong Custer at the Battle of the Little Bighorn in the Montana Territory in 1876.

Mr. Banks, whose early life of poverty, alcoholism and alienation mirrored the fates of countless ancestors, led protests that caused mass disorder, shootouts, deaths and grievous injuries. He was jailed for burglary and convicted of riot and assault, and he became a fugitive for nine years. He found sanctuary in California and New York but finally gave up and was imprisoned for 14 months.