Judge Stephen Reinhardt, a liberal stalwart on the U.S. 9th Circuit Court of Appeals for nearly four decades, died Thursday in Southern California. He was 87.

Reinhardt died of a heart attack during a visit to a dermatologist in Los Angeles, court spokesman David Madden said.

"As a judge, he was deeply principled, fiercely passionate about the law and fearless in his decisions," 9th Circuit Chief Judge Sidney Thomas said in a statement. "He will be remembered as one of the giants of the federal bench."

Reinhardt was appointed by President Jimmy Carter in 1979 and went on to become the sixth longest-serving judge on the court.

He was considered to be one of the most liberal judges on the 9th Circuit and his rulings often placed him on the side of immigrants and prisoners. Reinhardt wrote a 2012 opinion striking down California's gay marriage ban.

He also wrote a 1996 opinion that struck down a Washington state law that prohibited doctors from prescribing medication to help terminally ill patients die.

Last year he wrote in an opinion that a Trump administration order to deport a man who entered the country illegally nearly three decades ago and became a respected businessman in Hawaii was "inhumane" and "contrary to the values of the country and its legal system."

Reinhardt was "brilliant - a great legal mind and writer - but he was equally hard working," said Hector Villagra, executive director of the American Civil Liberties Union Foundation of Southern California.

Villagra, who clerked for Reinhardt in 1995, said he once found the judge in his chambers at 11 p.m. on a Saturday writing a dissent to the court's decision not to rehear a death penalty appeal.