Rejecting a government proposal that the island be turned into a park with “maximum Indian qualities,” Mr. Trudell said: “We will no longer be museum pieces, tourist attractions and politicians’ playthings. There will be no park on this island because it changes the whole meaning of what we are here for.”

Image Mr. Trudell in 2005. Credit... Carlo Allegri/Getty Images

The F.B.I. compiled a substantial file on him.

In 1979, Mr. Trudell burned an American flag on the steps of the F.B.I. building in Washington, saying that the flag had been desecrated by the government’s behavior toward American Indians and other minorities, and that burning was the appropriate way to dispose of a desecrated flag.

The next day, his home in Nevada burned to the ground. The fire killed his pregnant wife, Tina Manning, who was also an activist, as well as their three children and Ms. Manning’s mother.

An investigation by the Bureau of Indian Affairs found that the fire was an accident. But some viewed the inquiry as perfunctory, and its findings were questioned by an investigator hired by Mr. Trudell, who suspected the fire had been deliberately set.

“I don’t want to say that the F.B.I. kills innocent kids and children,” Lindsey Manning, a cousin of Tina Manning, said in “Trudell,” an acclaimed 2005 documentary film by Heather Rae. “I just don’t want to say that. But you never know. You never know.”

The film asserted that the cause of the fire had never been established.

John Francis Trudell was born in Omaha on Feb. 15, 1946, and grew up partly there and partly on a reservation near the South Dakota border. His father, Clifford Trudell, was a Santee Dakota; his mother, the former Ricarda Almanza, was of Mexican-Indian descent. She died when John was a boy.