Butler died peacefully in his sleep, sheriff's Capt. Ben Wolfinger told The Associated Press. The time of death was not immediately known.
"Everything appears to be natural," said Wolfinger, of the Kootenai County, Idaho, sheriff's department.
The Aryan Nations lost its church and 20-acre compound in northern Idaho in 2000 after a $6.3 million civil judgment led to a bankruptcy filing. He moved into a house bought by a supporter in nearby Hayden, Idaho, and made few public appearances in recent years because of failing health.
But in July he rode in the back of a pickup truck that was dragging the flag of Israel during a parade by about 40 of his followers through downtown Coeur d'Alene, 30 miles east of Spokane.
Butler, a longtime admirer of Adolf Hitler and white supremacist religious teaching, had moved to Idaho in the early 1970s, claiming later that he was impressed by its high percentage of white residents. To the dismay of many locals, the region became known as a place hospitable to white supremacist groups.
Butler's church held that whites are the true children of God, that Jews are the offspring of Satan and that blacks and other minorities are inferior.
The compound drew skinheads, ex-convicts and others from the fringes of society. Over the years, Butler's disciples included some of the most notorious figures in the white supremacist movement.
In the 1980s, followers who called themselves The Order committed a series of armored car robberies and bombings, and murdered Denver talk radio host Alan Berg. In 1985, 10 Order members were convicted of racketeering and other charges.
Other followers included Randy Weaver, whose wife and son were killed in a 1992 shootout that also killed a deputy U.S. marshal, and Buford Furrow, a former Aryan Nations security guard who killed an Asian-American postal carrier and shot up a Jewish day care center in Los Angeles in 1999.
In a 1999 report, the FBI said the goal of Aryan Nations was to forcibly take five states — Oregon, Idaho, Wyoming, Washington and Montana — and form an Aryan homeland.
Butler's undoing began in 1998, when Aryan Nations security guards chased a car they thought had fired a gun at them. It was apparently a backfire or firecracker.
The guards fired repeatedly at the car, shooting out a tire and forcing it into a ditch. One of them grabbed the driver, local resident Victoria Keenan, jabbed her ribs with a rifle butt and put a gun to her head.
Keenan and her son, Jason, sued Butler, arguing his organization had been negligent in its supervision of the guards. In 2000 they won a $6.3 million judgment. They were aided by the Southern Poverty Law Center, which called Butler the "elder statesman of American hate."
"They cannot run me out of northern Idaho with my tail between my legs," Butler said after the judgment was announced.
But Butler filed for bankruptcy and the Keenans gained possession of the compound. They sold it to the Carr Foundation, a human-rights group that demolished the buildings and donated the property to a college.
Butler, born in Colorado and trained as an aeronautical engineer, claimed he became admirer of Hitler while serving the United States Army Air Corps during World War II. He said Hitler "led a nation, a division of our race, to fight for the life of our race."
For years, law enforcement officers tried but failed to tie Butler to crimes by his supporters. In 1987, an Arkansas grand jury indicted Butler and others on charges of seditious conspiracy to overthrow the government by acts of violence. But the defense contended a key prosecution witness made up his story, and all were acquitted.