Jack Kevorkian, the assisted-suicide crusader, died early Friday morning in a Michigan hospital.
"It was peaceful. He didn't feel a thing," his lawyer, Mayer Morganroth, told The Detroit Free Press.
Mr. Kevorkian, an 83-year-old retired pathologist, had been hospitalized for pneumonia and kidney problems.
An official cause of death has not been determined, but Mr. Morganroth said it likely will be pulmonary thrombosis.
"I had seen him earlier and he was conscious," Mr. Morganroth told The Associated Press, adding that the two spoke about Mr. Kevorkian's pending release from the hospital and planned start of rehabilitation. "Then I left and he took a turn for the worst and I went back."
Nurses at William Beaumont Hospital in Royal Oak played recordings of classical music by composer Johann Sebastian Bach for Mr. Kevorkian before he died around 2:30 a.m., Mr. Morganroth said.
The right-to-die advocate known as Dr. Death claimed participation in at least 130 assisted suicides in the 1990s.
He was convicted of second-degree murder in 1999 for helping a terminally ill patient kill himself. He spent eight years behind bars.
While in jail, Mr. Kevorkian said he still believed in assisted suicide but would not choose it for himself.
"Remember that I did not advocate assisted suicide," he said in a written response to a question from The Detroit News in 2006. "I only advocated that a person should have the right to have the option if he or she, in sound mind, needed and desired it while in irremedial pain and suffering and terminal."
Throughout the 1990s, Mr. Kevorkian challenged authorities to make his actions legal, or try to stop him.
"You think I'm going to obey the law? You're crazy," he said in 1998 shortly before he was accused, and then convicted, of murder after injecting lethal drugs into Thomas Youk, 52, a suburban Detroit man suffering from Lou Gehrig's disease.
Mr. Kevorkian videotaped that death and sent the footage to 60 Minutes, which aired it. He challenged prosecutors to charge him. They did and he was given a 10- to 25-year sentence for second-degree murder. He earned time off his sentence for good behaviour.
Mr. Kevorkian, who was stripped of his medical licence, ran for Congress in 2008 as an Independent, receiving just 2.7 per cent of the vote in the suburban Detroit district. He said his experience showed the party system was "corrupt" and "has to be completely overhauled from the bottom up."
Mr. Kevorkian was the subject of a 2010 HBO movie called You Don't Know Jack, which earned its star, Al Pacino, Emmy and Golden Globe Awards.
With a report from The Associated Press