David Finn, a dominant figure in the creation of the modern public relations industry as the co-founder of Ruder Finn, one of the most successful corporate P.R. firms to emerge after World War II, died on Monday at his home in New Rochelle, N.Y. He was 100.

His granddaughter Rachel Spielman confirmed the death.

Mr. Finn was a public relations counsel to such corporate giants as Lever Brothers, Exxon, Bristol-Myers Squibb, Novartis and Coca-Cola. He was also devoted to the arts as a painter, illustrator, photographer and sculptor (notably using paper clips as his medium), and persuaded many of his clients, including the tobacco maker Philip Morris, to support the arts.

Mr. Finn did promotional work as well, some of it pro bono, for organizations like the United Nations, the Vatican, the World Bank and Springs Industries, a textile manufacturing company, which, at his prompting, became a major sponsor of photography and art exhibitions in the United States.

He often said that he “didn’t go into business to make money.” Nonetheless, by 1967, Ruder Finn had grown into the world’s largest P.R. agency at the time.

“I would put him among the top five on the Mount Rushmore of modern public relations, along with Harold Burson, Daniel Edelman, Al Golin and Gershon Kekst,” Larry Weber, the founder and former chief executive of Weber Shandwick, one of the world’s largest P.R. firms, said in an interview for this obituary this year.

Mr. Finn was at the forefront of a wave of former G.I.s entering the public relations field after World War II. He and a childhood friend, Bill Ruder, started the firm in 1948 and got their first big break when they were introduced to an aspiring young crooner and former barber named Perry Como.

The agency proceeded to jump-start Como’s career, promoting his albums to radio stations and creating clever contests for DJs as a way to get them to play his records. Within a year, Billboard magazine had named Como the country’s most popular recording artist.

The agency’s success with Como attracted more show business clients, including Dinah Shore, Burl Ives, Jack Lemmon, Eydie Gorme and the Mills Brothers. Corporate clients followed, and in time Ruder & Finn, as the firm was then known, swung its attention in their direction.

Mr. Finn, who was long outspoken about maintaining ethical standards in business, found himself in a controversial position while working with Philip Morris after the release of the Surgeon General’s report linking cigarette smoking to cancer in 1964.

For years, tobacco companies had denied that cigarettes caused harm, but several Ruder & Finn employees nevertheless expressed uneasiness about working with Philip Morris. Mr. Finn convened an agency ethics committee to discuss the issue, and it concluded that Philip Morris had sponsored enough community-oriented activities to justify a continued relationship.

In magazine articles and later in a book, “The Corporate Oligarch” (1969), an insider’s look at the corporate world, Mr. Finn said he had tried to walk a fine line between urging Philip Morris to come clean about the dangers of smoking and not destroying his firm’s business relationship with the company.

“Too often, I thought, businessmen hired public relations people with the expectation that they would be able to stifle their critics, and I felt that this was misguided,” he wrote. “Criticism was one of the inevitable features of a free society, and businessmen needed to listen to and respond constructively to criticism rather than try to suppress it.”

In a 1968 study for Philip Morris, Ruder & Finn suggested that the company “stop fighting the Surgeon General” and accept the medical data. The report recommended that Philip Morris work toward making a safer product and ensure that its advertising didn’t target young smokers.

But by publicly confronting Philip Morris in articles and books, Mr. Finn strained his relationship with the company.

“He was very outspoken, and he became not very welcome as part of the team at Philip Morris,” said Mr. Finn’s daughter Kathy Bloomgarden, who became chief executive of the firm when her father retired in 2011.

He was born David Finkelstein in New York on Aug. 30, 1921. His father, Jonathan, was a writer who used Finn as a pen name and then legally changed the family name to Finn when David was in high school. His mother, Sadie (Borgenicht) Finn, made children’s dresses.

Along with his older brother, Herbert, and his younger sister, Helen, David grew up on Broadway at 110th Street in Manhattan. He began painting at a young age and took to sketching fellow subway passengers on his way to high school in the Bronx.

He and Mr. Ruder, whom he had met when they were 11-year-old Hebrew school classmates, both entered the City College of New York in 1939. When the war began, he joined an Army Air Forces program that allowed him to finish school before joining the ranks. He earned his bachelor’s degree in 1943. By the time he shipped out, however, the war in Europe was over, and he was home in two months.

His sister, Helen, married Mr. Ruder, and she introduced Mr. Finn to Laura Zeisler, a Hunter College classmate. They married in 1945 and had four children, all of whom eventually worked at Ruder Finn.

In 1948, Mr. Finn and Mr. Ruder came up with the idea of using fine art to help companies promote their products. The business they founded, Art in Industry, operated out of a former linen closet in the Lombardy Hotel in Midtown Manhattan. But the idea bore little fruit, and they began to cast a wider net for clients. It was then that an uncle of Mr. Ruder’s introduced them to Como’s lawyer, who hired them to promote his client for $100 a week (about $1,200 today).

While expanding the company, with offices in Midtown, Mr. Finn furthered his involvement in the arts, painting and sculpting on weekends and in the evenings and, in his travels around the world to recruit clients, visiting museums and gardens.

He was 40 when he got his first camera and began photographing the sculpture he saw, becoming so adept at it that he went on to publish or contribute photographs to more than 100 books. (Among his own titles are “How to Visit a Museum” and “How to Look at Sculpture.) Many of his photographs are housed in the National Gallery of Art library.

Mr. Finn was an early supporter and promoter of the English sculptor Henry Moore and was instrumental in introducing his work to Americans. The two formed a lasting friendship.

Mr. Finn was particularly known for making elaborate metal sculptures in his office using straightened paper clips.

“His art influenced his thinking about creative campaigns,” said Shelley Spector, a co-founder of the Museum of Public Relations in New York and a former Ruder Finn executive. “His office was like an art museum, and his photography meant more to him than the business side.”

He also wrote for many business and general interest magazines, including Forbes, Fortune, Harper’s, Saturday Review and Harvard Business Review.

Mr. Finn caused an internal uproar at his firm when, in the 1980s, he promoted three of his children into management roles at the firm. Complaining of nepotism, three senior managers and 11 others left to join a rival firm, taking with them Ruder Finn’s biggest accounts. But Mr. Finn, who had declined numerous offers to be acquired by other firms, defended the move, saying he wanted to ensure that the agency would remain independent and under family control. Within three years, revenues reached a new high.

Mr. Ruder had left the firm in 1980 but had remained on the board. He died in 2011.

In addition to his daughter Ms. Bloomgarden and his granddaughter Ms. Spielman, Mr. Finn is survived by his wife; two other daughters, Dena Merriam and Amy Binder; a son, Peter; nine other grandchildren; and 20 great-grandchildren.

Ethics in public relations remained a consuming interest to Mr. Finn, and he spoke and wrote about it frequently. In one lecture, in 1995, titled “Ethical Dilemmas in Communications,” he told the Institute for Public Relations that “being public relations counsel to a client carries with it the responsibility to believe that what one’s client says is in fact true.”

“If my name is on a press release,” he said, “I should stand behind the legitimacy of what is stated in the release.”