Clarence M. Ditlow, III, one of the most influential and effective consumer activists of the past five decades, died Thursday in Washington, D.C., of colon cancer. He was 72.

Ditlow was the longtime executive director of the Center for Auto Safety, a watchdog group founded in 1970 by Ralph Nader and Consumers Union, now the policy and mobilization arm of Consumer Reports. He leaves behind an astonishing legacy of work on safety defects that led to the eventual recall of tens of millions of vehicles.

He was at the center of every major automotive safety controversy dating back to the exploding gas tanks of the Ford Pinto during the disco era, and as recently as this summer remained a strong voice for how to regulate autonomous technology in vehicles.

“He was the nightmare of the misbehaving auto industry and the dream of safety-conscious motorists,” Nader said of Ditlow in an interview with the New York Times in October. “He was also honest, ethical, and self-effacing.”

Mentored early in his career by Nader, Ditlow was never afraid to challenge the status quo and often refused to back down until he got results. He could be equally hard on automakers and regulators charged with governing the industry.

"He was one of the great consumer advocates in America,’’ said Joan Claybrook, a former Consumers Union board member and president emeritus of Public Citizen. "I can’t think of a single example of a time he thought there was a problem that he didn’t prove he was right and force action on it.”

Clarence Ditlow had a hand in exposing nearly every major case of automotive malfeasance since Richard Nixon inhabited the White House.

Here’s a partial list: exploding Ford Pintos, failing Firestone 500 tires, GM’s fire-prone C-K pickups, Ford Explorers that rolled over after their Firestone tires lost their treads, Toyota’s unintended acceleration, GM’s faulty ignition switch, and Takata’s exploding airbags.

And thanks mainly to Ditlow, so-called lemon laws have been adopted throughout the country that enable consumers of cars and other goods to be compensated when products fail to meet basic standards of quality and performance.

“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 Mark Rosekind, director of the National Highway Traffic Safety Administration (NHTSA). “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.”

Read more about car safety, including the Takata airbag recall and cars with advanced safety systems.  

Ditlow began working with Nader and Claybrook in 1971 soon after Nader established a network of consumer groups, including the U.S. Public Interest Research Group (or PIRG).

He was an engineer by training with a law degree from Georgetown University, and had recently finished a master’s degree in environmental law at Harvard when he became one of the first people hired to carry on the movement Nader started with the book, “Unsafe at Any Speed.”

In it, Nader called out General Motors for marketing a two-door coupe, the Chevrolet Corvair, that was prone to roll over. Nader went on to show how many common features of automotive design at the time were linked to predictable, preventable traffic deaths.

Consumers Union and Nader joined forces to establish the Center for Auto Safety—with a mission to protect the public from potentially fatal design flaws.

Claybrook needed someone with technical expertise to work with her at PIRG, and says that’s why Ditlow first appealed to her. But early on, he was shy and quiet and quite unlike many of the other noisy activists that became known as Nader’s Raiders.

Still, Claybrook was convinced he could help the cause, and remembers persuading Nader to hire him, in part, because Ditlow had been a competitive wrestler. Anyone who’s been a wrestler has been a bulldog, she told Nader.

"Boy, was I right,” she told Consumer Reports.

Ditlow soon proved to be the perfect complement to Claybrook’s louder and more public-facing persona—backing up sometimes difficult-to-believe allegations with meticulously compiled technical documentation.

"When you look at his 40 years of contributions, he has a legacy that will be hard for anyone to match,’’ said Jackie Gillan, president of Advocates for Highway and Auto Safety in Washington, D.C.  

Ditlow began directing the Center in 1974 and in 1978 replaced Nader on Consumer Union’s board of directors, where he served until 2011.

"Clarence Ditlow lived a life of tremendous consequence for the millions of people whose own lives were made safer because of his ceaseless determination," said Marta L. Tellado, president of Consumer Reports. "The victories he won on behalf of the consumer interest have made a true difference to families across the country, and will be felt for generations to come."

Read more about the issues that matter to Consumer Reports.

In the 1970s and 1980s, Ditlow developed a reputation for being a tireless investigator of public documents and hidden clues. He read everything and if something sounded strange to him, he dug deeper and asked more questions.

He used his engineer’s brain to discover safety defects that were often hiding in plain sight in automaker reports to NHTSA, or buried in consumer complaints to the agency’s hotline. He went over crash reports in federal databases. He used his legal skills to mine lawsuits for admissions from company executives about what they knew was happening behind the scenes.

As a particular defect came into focus, Ditlow and the Center built case files thousands of pages long. They’re available to the public to this day on the Center’s website, and the list reads like a who’s who of automotive controversies: Ford transmissions that could slip from park to reverse in the 1970s; GM brakes that could lock up in the 80s; fuel-tank fires in pickup trucks in the 90s; SUV rollovers in the 2000s; and sudden-unintended acceleration in Toyota vehicles in 2010.

Ditlow’s ability to dig and connect the dots, and explain what was going on in a clear, simple way made him a potent foe of the auto industry.

Initially, many tips came from the thousands of letters sent to Nader from consumers claiming their cars were defective. Eventually, the Center got its own members writing in. He also had a network of engineers, lawyers, and professors who spotted automaker wrongdoing and alerted him.

"He could tell when people were cheating,’’ Claybrook said.

He may not have been as comfortable in front of Congress or a television camera as in the warren-like offices of the Center, but Ditlow did more than his share of public and media appearances. He made sure reporters understood the documents and learned how to deliver the publishable quote.

He had a great ability to communicate, said Jack Gillis, author of the Car Book, an annual guide to fuel economy and safety information published by the Center for Auto Safety.

"It was because he was a brilliant person,’’ Gillis said. "Taking complex ideas and putting them into simple terms is very difficult. He could take very tough technical issues, or policy, or regulations, and boil them down into two or three sentences."

The media crush that surrounds congressional hearings such as those on the Ford-Firestone rollovers, the GM ignition-switch deaths, or exploding Takata airbags can be intense. But Jack Gillis says those were the times Ditlow was the happiest, because his work was making a difference.

"It was what he lived for,” Gillis said. "There’s no question he has been the leader on auto safety in the consumer movement,’’ he added. "There are relatively few people who have improved the public health of Americans more than Clarence Ditlow."

Such work didn’t endear him to automakers or regulatory agencies. He complained when documents were missing from the public record, and pushed regulators with petitions for more rulemaking and by calling for defect investigations. He filed a continuous stream of lawsuits to make sure government records on auto defects became public information under the Freedom of Information Act.

Those same officials conceded that even though he was one of the most difficult people they had to deal with, Ditlow helped them do their jobs. He pointed out things that the agency had missed.

One reason Ditlow was effective is that he focused on defects that exposed larger problems, said Sean Kane, president of Safety Research and Strategies, a public-interest legal research firm in Rehoboth, Mass. Ditlow’s biggest wins were cases that involved unsafe vehicles that complied with U.S. safety laws even though their occupants were getting killed, Kane said.

"Clarence had a penchant for these large issues that pushed the envelope, particularly those that showed the weakness of the regulatory agencies,’’ Kane said.

Ditlow used those examples to show how NHTSA’s regulations were out of date, then testified on Capitol Hill to make sure lawmakers knew. He also tirelessly fought with NHTSA to make automaker data available to the public.

One of his campaigns was about the technical service bulletins car companies send to dealers. Those alerts can often flag safety defects that have yet to be identified with a formal recall. The companies are required by law to send copies to NHTSA but not the wider public. After years of Ditlow, prodding, the reports are now searchable on the agency’s website.

"We shouldn’t have these kinds of government secrets,’’ Kane said. "Clarence knew that. These were small, behind-the-scenes maneuvers, but the outcome has been a significant benefit for the public.’’

Whomever succeeds Ditlow at the Center for Auto Safety will have a strong blueprint to follow, Gillis said.

"I don’t know what I’m going to do without him,’’ Gillis said. "My only hope is there’s another Clarence Ditlow out there, someone dedicated to what’s right and willing to follow the leads wherever they might go.’’