Assisted suicide advocate and retired physician Jack Kevorkian died Friday in a Detroit-area hospital. He was 83.

Kevorkian was being treated for heart and kidney problems at William Beaumont Hospital in Royal Oak, MI, and died after a blood clot broke free and lodged in his heart, the Detroit Free Press reported.

"It was peaceful, he didn't feel a thing," longtime Kevorkian attorney Mary Morganroth told the newspaper.

Kevorkian, a retired pathologist, came to be known for his advocacy of assisted suicides, and claimed to have assisted at least 130 of them by helping patients administer fatal chemicals through a machine he called a thanatron.

In an interview with CNN last year, Kevorkian said he had no regrets about helping suffering patients die.

"No, no. It's your purpose, your position," Kevorkian said. "How can you regret helping a suffering patient?"

Sometimes known as Dr. Death, he gained the national spotlight in 1990 by assisting in the suicide of a 45-year-old Alzheimer's disease patient, Janet Adkins, in his own Volkswagen van in a Michigan park.

According to reports, Adkins administered the fatal dose, dying of heart failure within minutes. The state of Michigan ruled her death a murder and charged Kevorkian.

The case was later dismissed, leading to changes in Michigan's assisted suicide laws.

The state closed one loop hole as Kevorkian found another until 1998 when the Michigan legislature passed a law making assisted suicide a felony.

In that same year, the CBS news show 60 Minutes aired a video of Kevorkian assisting a patient's suicide. After the footage aired, Kevorkian dared the courts to pursue him, and they did.

In 1999, Kevorkian was convicted of second-degree murder and the illegal delivery of a controlled substance, and was sentenced to 25 years in prison.

After eight years and numerous failed appeals, he was released from prison on good behavior.

On being in jail: "Well, it wasn't that hard, because I knew I wasn't a criminal. Most of the inmates and guards supported me. Some of them actually protected me. They knew I wasn't a criminal, and they knew what I did wasn't a crime. Everybody knows it," Kevorkian said to HBO.

Kevorkian's story was recently told in the 2010 HBO film, You Don't Know Jack.

For his portrayal of Kevorkian, actor Al Pacino won an Emmy, a Golden Globe and a SAG Award.

In an interview with HBO, Pacino said playing Kevorkian taught him how humorous and intelligent the doctor was. For example, Pacino said during court appearances, Kevorkian spent time teaching himself Japanese.

But Pacino said he also learned how much Jack wanted to be there for people.

"His patients and their families felt more comfortable and safer when he was administering euthanasia," Pacino said. "They could've done it by themselves, but they would've been upset because they wouldn't know what to do if it went wrong. They were so fearful of that. He was there, because it gave them a comfort zone."

Kevorkian was born May 26, 1928, in Pontiac, MI.