When Pat Moore was on duty at P.J. Clarke’s, the gaslight-era saloon in Midtown Manhattan, there was no question about who would wait on the most tables that day, or be requested by the greatest number of customers, or close out the shift with the highest check average.

Nor was there any doubt that Ms. Moore would remember every plate of food and every drink that every person at every one of her tables had asked for, without writing down any of it. Many customers didn’t need to ask because she had long ago committed their preferences to memory, along with their names: Johnny Depp. Andre Agassi. Frank Sinatra. Brooke Shields. Tony Bennett. George Steinbrenner. Peter Lawford.

During a career at P.J. Clarke’s that lasted at least 45 years — possibly longer, though nobody is sure — Ms. Moore became a landmark within a landmark, as much a part of the atmosphere there, on Third Avenue at East 55th Street, as its leaded-glass transom windows and framed portraits of Abraham Lincoln. She had the longest tenure of any of its employees in the modern era, or perhaps any era. (The saloon opened in 1884.)

Long after her 80th birthday, Ms. Moore continued to walk the six blocks from her apartment on East 50th Street to the restaurant and back again at least three days a week. Recently, another server there turned 65 and, as many people do at that age, decided to retire. At the going-away party, Ms. Moore made her disapproval known.

“You’re making a big mistake,” she told the woman. “You’re too young.”

For her part, Ms. Moore said, she planned to work until she was 90. She almost made it.