Ralph Nader, founder of the Center, hailed Ditlow's achievements on Friday: "He was a giant in the causes of safer, more fuel efficient, less polluting motor vehicles, a 24/7 watchdog of the auto industry. He brought his engineering and legal skills to bear on the meticulous details of auto industry regulation and defect recalls. He held both industry and NHTSA accountable for their respective life saving missions.
"There would be many motorists who would not be as safe now. Clarence Ditlow was their exceptional guardian angel."
No one was spared his scrutiny. Carmakers and the National Highway Traffic Safety Administration alike took heat from the relentless watchdog, the son of a Chevrolet dealership service manager.
Just this summer, while ailing with colon cancer, Ditlow took NHTSA to task over the issue of autonomous vehicles after a man was killed when his Tesla Model S collided with a truck.
"In its zeal to advance vehicle electronics, NHTSA has forgotten it is a regulatory agency to ensure vehicle safety, not a promotional agency to foster the development of new vehicle technology," he wrote in a letter to NHTSA Administrator Mark Rosekind.
Rosekind said Ditlow improved safety for anyone riding or driving a motor vehicle.
"Clarence was relentless in his pursuits, and whether he was taking the fight to the auto industry, or prodding NHTSA when he felt we weren't moving fast enough, no one could ever doubt his heartfelt motivation," Rosekind said in a statement. "Americans are driving in cars that are safer thanks to Clarence, and his voice as an advocate for safety won't easily be replaced."
Said Nader: "He was really shy socially, but he wasn't shy about holding the car companies' feet to the fire, which was the reason nobody could dislike him. They respected that."
Indeed, his adversaries found the soft-spoken Ditlow hard to hate even though he was often a thorn in their side.
In a speech in May honoring the 50th anniversary of Ralph Nader's book Unsafe at Any Speed, Ditlow got a laugh from the crowd when he recalled once telling Lee Iacocca over lunch: "You make them, and I recall them."
Ditlow was a workaholic, often putting in time at the office seven days a week.
"He neglected a lot of personal things about himself," Nader said.
He finally married his longtime companion, Marilyn Hermann, on Oct. 22, 2016. They had gotten to know each other in 1979 when she was working for the EPA.
Claybrook, now chairman emeritus of Public Citizen, said she had urged Ditlow to finally get married. "For about 30 years. Clarence didn't have time to stop working to get married. We had the wedding in the hospital. We got streamers and balloons."