Jack Kevorkian, the retired pathologist who gained fame as the leading advocate of assisted suicide, died at a William Beaumont Hospital in Royal Oakon, Mich., on Friday at the age of 83.

The man nicknamed "Dr. Death" claimed to have assisted in at least 130 suicides from 1990 to 1999.

"Somebody has to do something for suffering humanity," Kevorkian once said. "I put myself in my patients' place. This is something I would want."

He was released from a Michigan prison in 2007 after serving eight years for second degree murder. 

Although his official cause of death has not been determined, close friend and attorney Mayer Morganroth speculated that Kevorkian died of pulmonary thrombosis.

He added his friend had been hospitalized since May due to pneumonia and kidney problems.