The Palm restaurant in Washington has become one of the city’s most venerable preserves of the power lunch, where lobbyists, politicos and the media elite gather to gnaw on steak and lobster and guzzle gossip and martinis.

The high priest of this “cholesterol temple,” as journalist Maureen Dowd once described the Palm, was Tommy Jacomo, who presided as manager and later executive director almost from the day it opened in 1972 until his retirement in 2016.

With his thick mustache and mastery of the convivial welcome, Mr. Jacomo was an out-front man in the mold of restaurateurs Duke Zeibert and Toots Shor, someone who greeted regulars by name and always knew their tastes and table preferences. He was the guardian of the restaurant’s wall of caricatures, controlling who made the grade for the highly coveted Beltway status symbol and who, alas, did not.

The former magazine publisher William A. Regardie, who like many longtime Palm patrons considered himself as much a friend of Mr. Jacomo as a customer, once called him “the most powerful man at the most powerful restaurant in the most powerful city in the world.”

Mr. Jacomo, 75, died March 6 at his home in St. Augustine, Fla. The cause was lung disease, said his wife, Kim Jacomo.

Working 12-hour days and running a more-than-40-year streak of working on New Year’s Eve, he served regulars that ranged from political consultants Mary Matalin and James Carville to TV personality Larry King, Redskins owner Jack Kent Cooke and entertainer Frank Sinatra. Boxer Muhammad Ali visited in 1976 and engaged Mr. Jacomo in a friendly sparring match; the manager later called it “the biggest thrill of my life.”

After a visit — just one for a president, perhaps a few dozen for a lobbyist — a customer might make it onto the Palm’s dining-room walls, where more than 1,000 caricatures are framed for diners to envy.

A drawing of President George H.W. Bush — who, while ambassador to the United Nations in the early 1970s, urged the restaurant’s New York owners to expand to Washington in the first place — shows him riding an elephant and wearing a loincloth.

“You’ve got to put some clothes on me,” Bush told Mr. Jacomo in 1994, according to an account by Dowd in the New York Times. “I was getting cold looking at my picture.”

Mr. Jacomo turned him down, saying, “If you ride an elephant, you don’t wear a tuxedo.”

The first Palm opened in Manhattan in 1926 as a conventional Italian pasta restaurant. Its name was an accident. The restaurant’s founders intended an homage to their hometown, Parma, Italy, but owing to their thick accents, the name was registered as Palm, without an article.

Mr. Jacomo descended from a family long ensconced in New York’s hospitality industry. His grandfather was chief steward at the Waldorf Astoria hotel, and his father was a bartender at the hotel’s renowned Bull & Bear steakhouse.

By the time the Palm’s third-generation owners asked Mr. Jacomo’s brother Ray to open the second location in Washington in 1972, the Palm had become synonymous with steakhouse opu­lence and four-pound lobsters.

Mr. Jacomo was running a motel restaurant in Vermont when his brother called to see if he would help in the new place. Expecting to work as a bartender, Mr. Jacomo ended up building some of the restaurant’s booths with plywood and a handsaw.

He was quickly named manager and replaced his brother as general manager when Ray Jacomo left to open a new Palm location in Miami Beach in 1989. There are now about 25 locations worldwide.

Tommy Jacomo’s style was “ruling with a silk glove,” one employee told the trade publication Nation’s Restaurant News in 2004. He made a point of keeping business and politics separate, telling the Times: “I didn’t know anything about politics when I got here. I learned real fast: Keep your mouth shut. And waffle.”

In 1977, Mr. Jacomo and a waiter were arrested for allegedly selling an ounce of cocaine to an undercover federal agent at the restaurant. They were among 20 people arrested in a five-month Drug Enforcement Administration operation that centered on sales at restaurants around the Palm’s Dupont Circle neighborhood.

Mr. Jacomo’s first call after the arrest was to criminal defense lawyer and Redskins co-owner Edward Bennett Williams, a Palm patron and friend with whom he sometimes traveled to Atlantic City boxing matches.

Williams put together a defense team from his firm, Williams & Connolly, which argued that while Mr. Jacomo had used and dealt cocaine in the past, he was not involved in this particular drug deal.

The federal prosecutor referred to Mr. Jacomo during the trial as the “maitre d’ of cocaine.” The defense team decided that Mr. Jacomo would do best to keep mum, out of fear he would light a cigarette or utter a profanity, according to a Times article by the conservative commentator and Palm crabcake enthusiast Tucker Carlson.

The waiter pleaded guilty, and Mr. Jacomo was acquitted of the charge. “You’re a very lucky fellow,” U.S. District Court Judge John H. Pratt told him.

One of the prosecutors, by Carlson’s account, later became a regular at the Palm.

Thomas James Jacomo was born in New York City on Aug. 3, 1944. As a young man, he said, he never intended to join the family business working in hotels or restaurants.

“I always wanted to be a mob guy,” he told the Times. He loved horse racing and for a while was a runner in the neighborhood numbers racket. But, he said, “I wasn’t tough enough. Those guys are tough.”

He dropped out of school at 15 and worked as a roofer. Three years later, his father got him a bar job at the newly opened New York Hilton.

Survivors include his wife of 39 years, Kim Rudowski Jacomo of St. Augustine; two daughters, Kendra and Jordan Jacomo; a brother; and a sister.

Running the Palm meant catering to demanding egos and taking intense interest in their culinary needs — and minimal interest in any hanky-panky.

“Charlie Wilson would be in here with three or four different ladies, and we wouldn’t tell anybody,” Mr. Jacomo told Washingtonian magazine about the late Texas congressman.

His discretion was rewarded, at times. In 1997, Mr. Jacomo was offered a prime spot at Cooke’s funeral, an event from which many prominent people were excluded — an indication of his standing in the city’s social pecking order.

What kept Mr. Jacomo in that place of honor, far more than his jocularity, was his competence and ability to adjust — profitably — when even the best-laid plans went awry.

In 2001, Mr. Jacomo prepared for a visit to the Palm by Russian President Vladi­mir Putin. His advance man said the president and his entourage wanted lobsters, so the restaurant staff took pains to prepare dozens of the crustaceans.

Putin arrived and promptly ordered steak. Everyone else in the group did the same.

Mr. Jacomo was unfazed, later saying, “We had lobster salad as the lunch special for the week.”