Assisted suicide advocate Jack Kevorkian, who spent eight years in prison for second-degree murder, died early Friday in a Detroit-area hospital after battling respiratory and renal problems, his lawyer confirmed to CBC News.

Mayer Morganroth said in a telephone interview from Birmingham, Mich., that he and Kevorkian's niece were by the 83-year-old's side when he died in Beaumont Hospital in Royal Oak.

"I was there all last night until he passed away," Morganroth said.

He added that Kevorkian had several problems that were treatable, including having a cancerous lesion on his liver but that could have been removed, and the respiratory and renal issues.

"But he had a pulmonary thrombosis [blood clot] that came to his lung, and that changed everything, and then it was a matter of hours before he passed away," between 2:30 a.m. and 3:30 a.m. ET.

Kevorkian had been admitted to hospital about two weeks ago. The hospital hasn't released an official cause of death.

The Armenian-American pathologist, who claimed to have assisted in 130 suicides, advocated the rights of the terminally ill, famously saying, "Dying is not a crime."

In 1999, Kevorkian, who became known by the nickname Dr. Death, began serving eight years of a 10- to 25-year prison term, and was released in 2007 on the condition he not offer suicide advice.

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Despite his controversial preachings, "I think the great majority were in [Kevorkian's] corner, no question about it," Morganroth said. "You always get that percentage that will go for anything and take an antagonistic position. But the very substantial majority ... will mourn his loss.

"He advocated [the right to die] right up to the end, however, he did not perform it," Morganroth said, adding that Kevorkian continued to lecture following his release from prison,and his last one was at UCLA in front of 1,800 people in February.

In 2008, Kevorkian also ran for Congress as an Independent, but received just 2.7 per cent of the vote in a suburban Detroit district.

Morganroth was a constant travelling companion of Kevorkian. They both attended awards ceremonies honouring the 2010 HBO movie You Don't Know Jack, which tells his life story and features Al Pacino in the lead role.

Pacino won both Emmy and Golden Globe awards for his portrayal of Kevorkian.

Reacting to Kevorkian's death, Canadian medical ethics expert  Udo Schuklenk, a professor at  Queen's University in Kingston, Ont., said he might disagree with his methods, but there's no question Kevorkian left a legacy in the U.S. on assisted suicide.

He said Kevorkian forced society to examine an issue it would like to sweep under the carpet — death and dying — and that debate translated into the decriminalization of assisted dying in several parts of the U.S.

But Schuklenk also decried Kevorkian's "Wild West attitude" and "appalling" way he helped put people to death in the public spotlight.

Morganroth said funeral plans haven't been made, but he expects it to be a private, small service in the Detroit area.

With files from The Canadian press