Lester Wunderman, often called the “father” of the direct-marketing industry, discusses graphics at his Madison Avenue office in 1978. (D. Gorton/New York Times)

Lester Wunderman, the advertising executive who perfected the strategy of reaching customers in their mailboxes, in their periodicals through magazine inserts and on the telephone with 1-800 numbers, forever altering the way companies do business through direct marketing, died Jan. 9 at his home in New York City. He was 98.

His son, Marc Wunderman, confirmed the death and said he did not know the cause.

Mr. Wunderman, whom Adweek called the “father” of the trillion-dollar direct-marketing industry, was described as a self-taught, self-made success story. After his immigrant father died on the cusp of the Great Depression, Mr. Wunderman finished high school at 16, left college to support his family and worked his way from a factory job to the highest ranks of Madison Avenue.

With his older brother, Irving, he co-founded the advertising firm Wunderman, Ricotta & Kline in 1958. When Mr. Wunderman retired four decades later, Wunderman Cato Johnson, as the firm was then known, had 69 offices in 39 countries and annual billings that exceeded $1.8 billion. His clients over the years included CBS, Geico, Ford, L.L. Bean, American Express and Microsoft.

Mr. Wunderman was quick to note that he did not invent direct marketing. “It was invented shortly after Adam and Eve,” he told the publication Strategy in 1997. “I did name it, though, because it was undefined.”

The essence of his strategy, which he articulated in the late 1960s and early 1970s, was to know a product’s consumers and potential consumers and to reach them in the places, at the times and in the ways most likely to make a sale.

The future of advertising, he argued, lay not in billboards visible to every driver on a stretch of highway or in a commercial jingle blasted indiscriminately at every listener of a radio program. Instead, businesses should collect detailed information on their audiences and target their advertising campaigns specifically to them.

“It was no longer, ‘Hey, you,’ ” he once told USA Today. “It was, ‘Hey, you, Mr. So-and-so.’ That’s a big difference.”

Working with a flower company that was among his early clients, he insisted that they keep careful track of who ordered roses and who ordered tulips, who made large purchases and who made small ones, who ordered only occasionally, such as on Mother’s Day or Valentine’s Day, and who ordered more regularly.

In such efforts, the advent of the computer proved revolutionary.

“A computer can know and remember as much marketing detail about 200 million consumers as did the owner of a crossroads general store about his handful of customers,” Mr. Wunderman once said in a speech posted on his website.

“It can know and select such personal details as who prefers strong coffee, imported beans, new fashions, and bright colors,” he continued. “Who just bought a home, freezer, camera, automobile. Who had a new baby, is overweight, got married, owns a pet, likes romantic novels, serious reading, listens to Bach or the Beatles.”

Such information in hand, Mr. Wunderman sought to make personal connections with customers. He did so through direct mail that reached customers at their home and through magazine inserts of interest to readers of particular publications. Insomniacs are well acquainted with the toll-free 1-800 phone numbers that he advertised on television, inviting potential buyers to speak — right then and there — with one of the operators standing by.

He counseled his clients that once a buyer’s business was earned, the company should endeavor to keep it with campaigns such as the loyalty rewards programs that he helped popularize.

Some of Mr. Wunderman’s techniques presaged the targeted advertisements of the Internet era and their concomitant concerns about privacy, a value he insisted that companies must respect. He considered spam bad business and viewed it as different from the ads that he distributed through direct mail.

“I didn’t think I was offending anybody,” Mr. Wunderman told USA Today. “By sending mail that knows something about their needs, wants and lifestyle, you’re doing them a service.”

Lester Wunderman, a son of Jewish immigrants, was born in the Bronx on June 22, 1920. His father, who was from Austria, worked in the fur trade. After his death, Mr. Wunderman’s mother, who was born in Romania, did clerical work to provide for her sons.

After studying at Brooklyn College, Mr. Wunderman joined his brother in starting an advertising firm called Coronet. According to an account in Investor’s Business Daily, the business failed when their largest client declared bankruptcy. The brothers then presented a more established New York agency with an unusual offer: Hire one brother, get the other one’s time free. The agency took it, keeping the Wundermans in the advertising business.

Mr. Wunderman joined Maxwell Sackheim & Co. in 1947, rising to become executive vice president. He was fired at one point but continued coming to work because he felt he had more knowledge to gain there.

“OK, you win,” Sackheim, the founder, told him after a month. “You can have your job back. I never saw a man who wanted a job more than he wanted money.”

Wunderman, Ricotta & Kline was acquired by Young & Rubicam in 1973 and merged with Cato Johnson in 1992. Earlier this month, Wunderman merged with the firm J. Walter Thompson to form Wunderman Thompson.

Mr. Wunderman wrote two books, “Frontiers of Direct Marketing” and “Being Direct: Making Advertising Pay.” In 1999, he was inducted into the Advertising Hall of Fame.

He was a noted photographer and collector of the artwork of the Dogon tribe of West Africa, which he donated to the Metropolitan Museum of Art in New York, among other institutions.

Mr. Wunderman’s marriage to Liljan Darcourt ended in divorce. Survivors include his wife of 43 years, Suzanne Oksman Cott, of New York City; two children from his first marriage, Marc Wunderman of Redding, Conn., and Karen Wunderman Cusworth of Cranbury, N.J.; three stepsons, Patrick Cott of Chicago and James Cott and Thomas Cott, both of New York City; and six grandchildren.

Reflecting on his success, Mr. Wunderman shared credit with the people he hired, who included not only advertising professionals but also poets and novelists, who he said could see past sales statistics to understand the buyers — the people — behind them.

“Our people were like astronomers,” he was quoted as writing. “It took mathematical skills to plot the solar system but imagination to grasp its meaning.”