Bob Gray, seen here in his Gray & Co. office in 1981, was considered one of the most influential lobbyists in Washington. He was “a kind of legend in this town,” a Washington Post reporter once wrote in a profile, “the man in the black tuxedo with snow-white hair and a smile like a diamond.” (Ray Lustig/The Washington Post)

Bob Gray, who died April 18 at 92, housed his elite lobbying firm, Gray and Co., in the Georgetown building known as the Power House. Once the site of generating facilities for the neighborhood’s trolley system, the edifice became, under Mr. Gray’s ownership, a center of political power that made him one of the most sought-after lobbyists in Washington.

To many observers of the inner workings of American politics, he embodied lobbying as it came to be practiced in the modern era.

A former aide to President Dwight D. Eisenhower, Mr. Gray joined the Hill & Knowlton public relations firm in 1961. As director of the company’s Washington office, he helped turn the company into an industry giant.

Two decades later, when President Ronald Reagan took office, Mr. Gray left Hill & Knowlton to found Gray & Co. He had worked on Reagan’s successful 1980 campaign, co-chaired his inaugural committee and became known informally during the administration as the “First Flack.”

Five years after the firm was founded, its billings reached $16 million — a quarter of Hill & Knowlton’s business — according to the New York Times. Like many other professionals of his stature, Mr. Gray reportedly commanded hourly rates of $350 or more.

The firm distinguished itself by delivering in tandem the traditionally separate services of public relations work and lobbying. Mr. Gray provided his clients with what The Washington Post described as “unabashed promotion” in the media. His travels on the social circuit were so extensive, he said, that he wore out two tuxes annually. He was a frequent escort of President Richard M. Nixon’s secretary, Rose Mary Woods.

He was “a kind of legend in this town,” a Post reporter once wrote in a profile, “the man in the black tuxedo with snow-white hair and a smile like a diamond.”

Mr. Gray was particularly well connected within the Republican Party and hired influential Democrats, including former Carter administration officials, to diversify his firm. Clients included the Kennedy Center for the Performing Arts, the Teamsters union and the Church of Scientology.

Farther-flung accounts included the Canadian and Moroccan governments, the Marxist Angolan government and the Haitian government under dictator Jean-Claude “Baby Doc” Duvalier, which had retained Gray & Co. to “improve the Haitian image.” Mr. Gray told Forbes magazine that he had been approached by the Libyan government but turned it down as a client.

Critics often describe lobbying as influence peddling, and some questioned Mr. Gray’s tactics. He attracted attention in the 1980s when his firm distributed video news releases that strongly resembled traditional news reports — and that several TV stations presented as such. Gray & Co. maintained that the firm had advised news outlets of the nature of the releases.

In 1992, he was the subject of the book “The Power House: Robert Keith Gray and the Selling of Access and Influence in Washington” by Susan B. Trento. Mr. Gray later unsuccessfully sued the author for defamation for her unflattering depiction of his dealings.

In response to the charge that lobbyists sell “access” to decision makers, Mr. Gray argued that his profession was misunderstood and that clients received valid services.

“If you have access, and I’m proud we do, it shows you are doing something right, not something wrong,” he told The Post. “Almost never have I had an issue worthy of the president’s time. If you take somebody to the White House just to show you can get in, you are not going to get in next time.”

In 1986, Hill & Knowlton (which by then had become a subsidiary of the JWT Group) acquired Gray & Co. for $21 million. Mr. Gray remained with the company as manager of the Washington office and chairman of the board until stepping down in 1992.

Robert Keith Gray was born in Hastings, Neb., on Sept. 2, 1921, said his niece. He served in the Navy during World War II and remained in the Navy Reserve, attaining the rank of commander, she said.

He received a bachelor’s degree in political science from Carleton College in Northfield, Minn., and a master of business administration degree from Harvard University in 1949.

Shortly thereafter, he came to Washington and found work with the Navy as a special assistant for manpower. Under Eisenhower, his positions included secretary to the Cabinet.

Mr. Gray wrote two books, “Eighteen Acres Under Glass” (1962), about his time in the Eisenhower administration, and “Presidential Perks Gone Royal: Your Taxes Are Being Used for Obama’s Re-election” (2012).

He moved from the Washington area to Florida about two decades ago. Survivors include his partner of 20 years, Efrain Machado of Miami Beach; and a sister. A niece, Robin McGrath, said that Mr. Gray died at a hospital in Miami and that the cause was heart ailments.

In an entry for the Who’s Who reference guide, Mr. Gray once explained his success.

“When the young man raised in all the solid, basic virtues of the small town breaks out of his provincial cocoon into the city, he finds its variety invigorating, its cultural smorgasbord rewarding, its people mix exciting,” he wrote. “The small-town work ethic is rise early and work hard. Add the stimulation of the city to that foundation and the result is high odds for career and lifestyle success.”