Horse Capture, a member of the Gros Ventre tribe, died April 16 of kidney failure, his family said.
Horse Capture was an author, archivist and curator at the Plains Indian Museum at the Buffalo Bill Historical Center in Cody, Wyo. He served as assistant professor at Montana State University, taught at the College of Great Falls and worked for the National Museum of the American Indian at the Smithsonian.
But his foremost passion was for the Gros Ventre -- also known as the A'ani, or White Clay People.
"What he did in his life, he did for his tribe," Kay Karol said of her husband. "He wasn't looking for fame or fortune. He was looking for a positive response for Indian people in a white world that still can be pretty discriminating."
Horse Capture was one of hundreds of protesters who filled the abandoned prison grounds of Alcatraz Island in the San Francisco Bay in 1969, while 14 Native American protesters occupied the prison itself, the Great Falls Tribune reported.
The protesters demanded the U.S. government's acknowledgment of its broken promises to Native Americans.
"I had to be part of it," Horse Capture later told his friend Herman Viola. "I realized that history was being made. This was the first time tribes from across the country had gotten together for a cause -- our cause."