Stuart M. Speiser, a foremost authority on aviation law who made headlines in the late 1960s as Ralph Nader’s attorney in a groundbreaking invasion of privacy suit against General Motors, died Oct. 4 at his home in Scottsdale, Ariz. He was 87.

The cause of Speiser’s death was a self-inflicted gunshot wound, his family said.

Nader said Speiser, who was based in New York for much of his career, was a “pioneer in aviation and torts law” who, case after case, won record settlements for his clients.

He recalled his former attorney as deeply persuasive, aided by “a voice like Humphrey Bogart — a G-man’s voice, as they say.”

Speiser was one of the first lawyers to use expert testimony from engineers and forensics specialists to re-create a crash scene to prove negligence and willful misconduct.

He successfully represented clients in many high-profile cases, including people whose relatives had died in the 1988 bombing of Pan Am Flight 103 over Lockerbie, Scotland, and relatives of those who had died aboard Korean Airlines Flight 007, which was shot down in 1983 over the Soviet Union.

Speiser’s best-known case started with a phone call to Nader, the consumer advocate and lawyer whose 1965 book “Unsafe at Any Speed” attacked the lack of safety standards for car manufacturers and the fatal design flaws of the Chevrolet Corvair.

Hoping to tar Nader, General Motors hired a private detective. Nader began receiving dozens of annoying and threatening phone calls. He said that the private detective tailed him and that, in what he considered an attempt to entrap him, women repeatedly approached him on the streets to solicit sexual favors.

In a televised Senate hearing on Capitol Hill in 1966, GM President James Roche apologized to Nader for any harassment the company’s investigation into his personal life might have caused him. Once Speiser heard the apology, he phoned Nader.

“I told Ralph I was sure GM expected to be sued and that they were probably prepared to pay a large sum, larger than any previous award, to bury their mistakes,” Speiser wrote in his 1980 book “Lawsuit.” He said that the potential payout would be “large enough to keep Ralph’s crusades going for years.”

Speiser said that GM would be the perfect target because the company’s image suffered after the publication of “Unsafe at Any Speed.” Furthermore, he wrote, Nader would serve as the “knight in shining armor, champion of the consumer, the last honest man, even a sex symbol.”

Nader and Speiser sued GM for compensatory and punitive damages.

Attorneys for GM tried multiple times to throw the case out of court by saying that the carmaker was not responsible for any wrongdoing.

Speiser proved that the independent private detective, Vincent Gillen, had acted directly on behalf of GM and used Gillen’s testimony to that effect against his employer.

More than two years after the suit was filed, GM agreed to pay Nader $425,000 — the largest out-of-court settlement in the history of privacy law.

Nader said he used the settlement money to found several public interest groups, including the Center for Auto Safety.

Speiser’s Nader-GM suit has been included in tort law texts across the country.

A Scottsdale police spokesman said Speiser appeared to have planned his death in advance. He had propped open the door to his home for authorities and left a memo explaining to his family that he wished to die with his sharp mind intact.