Harold Burson, a public relations giant who co-founded Burson-Marsteller and built it into one of the world’s largest PR firms, developing a reputation for deft crisis management that made him a favorite of embattled corporations and foreign governments, died Jan. 10 at a rehabilitation center in Memphis. He was 98.

The cause was complications from a fall, said Catherine Sullivan, a spokeswoman for what is now the PR firm Burson Cohn & Wolfe.

Soft-spoken and unassuming, Mr. Burson was considered a chief architect of the modern public relations industry, which he believed was as much about behavior as messaging. “In the beginning, top management used to say to us, ‘Here’s the message, deliver it,’ ” he once said, according to the textbook “Public Relations: Strategies and Tactics.” “Then it became, ‘What should we say?’ Now, in smart organizations, it’s ‘What should we do?’ ”

A 1999 survey by the trade magazine PRWeek named Mr. Burson the most influential public relations figure of the 20th century, a title he reluctantly accepted as “the prize for survival,” having outlasted so many of his peers. He met President Ronald Reagan for monthly lunches, logged 125,000 flying miles a year while serving as Burson-Marsteller’s chief executive and went to his Manhattan office each day well into his 90s, encouraging clients to treat him as an extension of their company.

Those clients included corporations — Coca-Cola, General Electric, McDonald’s and Merrill Lynch — as well as the British government, the Saudi royal family and the regime of Romanian dictator Nicolae Ceausescu. And although Burson-Marsteller offered everything from news conference preparation to the selection of wine for key dinner meetings, the firm was perhaps best known for its crisis-management work.

Mr. Burson advised Johnson & Johnson in the aftermath of the cyanide-laced-Tylenol murders in 1982, and two years later, he represented Union Carbide after a gas leak killed at least 2,000 people near its pesticide plant in Bhopal, India — an industrial disaster that ultimately killed thousands more and affected some 600,000 people.

“We are being paid to tell our client’s side of the story,” Mr. Burson told the New York Times that year. “We are in the business of changing and molding attitudes, and we aren’t successful unless we move the needle, get people to do something. But we are also a client’s conscience, and we have to do what is in the public interest.”

Mr. Burson began his career as a journalist, working as a newspaper copyboy and then paying his way through college as a stringer for the Memphis Commercial Appeal. He interviewed William Faulkner as a teenager, reported on the Nuremberg war crimes trials for the military’s American Forces Network and formed his own PR firm in 1946, concluding that public relations offered a more lucrative path than journalism.

Seven years later, he partnered with advertising executive William A. Marsteller to form Burson-Marsteller, offering an integrated service they called “total communications” from their offices in New York and Chicago. It became only the second international public relations firm after opening a branch in Geneva in 1961, and by 1984, it was the world’s largest PR firm by net fee income — then $63.8 million, with some 4,100 employees in 42 offices worldwide.

Mr. Burson traced the company’s growth in large part to the decision to expand internationally. But it undoubtedly benefited from exposure related to the Tylenol case, in which seven people in the Chicago area died as a result of apparent tampering with bottles of the pain reliever on store shelves. No one was ever charged with the murders, and copycat poisonings followed around the country.

Johnson & Johnson recalled 31 million bottles of Tylenol, at a cost of more than $100 million, and redesigned its bottles to include a foil seal and childproof cap, among other safety features that were announced at a Manhattan news conference meticulously planned by Mr. Burson. His firm worked to ensure that everything from the telephones to the bathrooms would be ready for a wave of arriving journalists.

The event went off successfully, but it was overshadowed by “one of those things that public relations people dread,” Mr. Burson said — an unexpected piece of breaking news, namely the death of Soviet leader Leonid Brezhnev.

Mr. Burson and his firm also worked with Pan Am after the bombing of Flight 103 over Lockerbie, Scotland, in 1988 and with repressive governments in Nigeria, Argentina and Indonesia. Its charm offensives and other efforts on behalf of those governments (and companies such as the cigarette giant Philip Morris) garnered notoriety in some quarters, with MSNBC commentator Rachel Maddow declaring in 2012, “When evil needs public relations, evil has Burson-Marsteller on speed dial.”

Mr. Burson rejected that characterization, declaring that companies and governments had a right to representation — and that he and his firm were not above turning down clients over ethical concerns. In recent years, it rejected the Libyan government as well as a “major oil company” trying to lift sanctions on Iraq, he told PRWeek in 2014. “And,” he continued, “we said no to the National Rifle Association.”

The son of English immigrants, Harold Burson was born in Memphis on Feb. 15, 1921. His father ran a hardware store that closed during the Depression, leading his mother to support the family by selling clothing door to door.

A precocious reader, Mr. Burson started school in the third grade, graduated from high school at 15 and studied English and economics at the University of Mississippi while writing for the Commercial Appeal, filing stories at a rate of 14 cents per inch.

He received his bachelor’s degree in 1940 and, after reporting on labor problems surrounding the construction of a new munitions plant in Tennessee, was hired by the builder to do public relations. He spent more than two years at the construction firm, H.K. Ferguson, before joining the Army in 1943.

Mr. Burson later served on the board of groups including Kennedy Center Productions in Washington, where he was credited with soliciting $3 million from the Japanese government and private groups to construct the 500-seat Terrace Theater in the late 1970s.

In 1979, he sold Burson-Marsteller to the advertising agency Young & Rubicam, continuing to serve as the firm’s chief executive until 1988, one year after the death of Marsteller. The firm merged with Cohn & Wolfe in 2018 to form Burson Cohn & Wolfe.

His wife of 62 years, the former Bette Ann Foster, died in 2010. Survivors include two sons, Scott Burson of Lexington, Mass., and Mark Burson of Westlake Village, Calif.; and five grandchildren.

After turning 85, Mr. Burson began blogging about business and current affairs, an activity that he likened to “taking dope.” (“The more I blog, the more I like it,” he told the Dallas Morning News.) By then, he had become a gray-haired elder for his profession, with a poise and good humor that made him widely beloved, said his onetime client Geoff Bible, the former chairman and chief executive of Philip Morris parent company Altria.

“ ‘Make no enemies’ — I think that’s one of the great lines I heard in my life,” Bible told Ad Age magazine in 2012. “I must have made a million, and he made none.”