Robert Leopold Spitzer, a psychiatrist who played a defining role in creating agreed-upon standards to describe mental disorders and helped stop the defining homosexuality as a pathological condition, died Friday in Seattle. He was 83.

Spitzer died from complications related to heart disease, his wife, Janet Williams, reportedly said. He also suffered from Parkinson’s disease. Spitzer was born May 22, 1932, in White Plains, New York. He and Janet, his third wife, moved to Seattle from Princeton, New Jersey, earlier this year. 

He was often called one of the most influential psychiatrists of the 20th century, largely for his work in the modern classification of mental disorders. He was chairman of the task force for the third edition of the American Psychiatry Association’s (APA) Diagnostic and Statistical Manual of Mental Disorders (DSM-III), which was released in 1980 and classified mental disorders in discrete categories with specific criteria to diagnose them.

Williams, who worked with Spitzer on DSM-III, said that the book “was a major breakthrough in the profession,” reported the Associated Press.

In the early 1970s, Spitzer met with gay-rights activists and determined that homosexuality could not be called a disorder if homosexuals were comfortable with their sexuality. At the APA conference in 1973, he pushed for the association to drop homosexuality as a medical disorder from its manual, signifying a major turning point for the gay rights movement.

“A medical disorder either had to be associated with subjective distress — pain — or general impairment in social function,” he told the Washington Post at the time, explaining his reasoning. Since gay people were comfortable and happy being gay, and functioned like everyone else in their daily lives, they did not suffer from any disorder, he reasoned.

In 2001, after two years of interviews with 200 "ex-gay" men and women who had been through sexual reorientation therapy, he concluded in a paper that gay people can turn straight if they really wanted to. In 2012, however, he publicly said that he wanted to redact that paper, stating that the study was flawed.

Some gay rights activists attribute the U.S. Supreme Court’s judgment allowing gay marriages partially to the work done by Spitzer.

“The fact that gay marriage is allowed today is in part owed to Bob Spitzer,” Jack Drescher, a gay psychoanalyst in private practice in New York, told the New York Times.