Letitia Baldrige, who has died aged 86, served as social secretary to Jacqueline Kennedy in the gilded JFK White House and then assumed a stately position as America's arbiter of class, taste and manners.
She dished out advice on everything from how to greet the Queen to what to do with a napkin ring once the napkin has been removed.
As times changed she informed the readers of her countless etiquette books on how to break free from the tyranny of the mobile telephone and computer screen and re-establish family conversation and good manners.
Above all she sought to preach the virtues of a little decorum as a brash new-money age of celebrity washed away the values of old.
"Many people feel we've lost all sense of taste," she noted in an interview with Women's Wear Daily in 2007, making no secret of the fact that she was one of them.
"Notoriety is what sells. As far as excellence, half the people don't even recognise it. These celebrity fashion icons, if they have screamingly bad taste, no one seems to care. When [Barbra Streisand] wears nightgowns for her fourth wedding and puts her bosoms in people's faces, everyone thinks that's the way to behave."
Jacqueline Kennedy, by contrast, "did not know a moment of bad taste".
Letitia Baldrige, always known as Tish, was born on February 9, 1926, to the future Republican congressman Howard Baldrige and his wife Regina.
Tish grew up in Omaha. She attended Miss Porter's private school in Farmington, Connecticut, and it was there that she first met Jacqueline Bouvier. From the off she was a friend and admirer of the future First Lady.
"Her classic good looks were complemented by her sense of style. Nothing ever looked wrong on her," she wrote later.
The two were classmates again at Vassar, the liberal arts college in New York State before, in 1946, Baldrige travelled to Switzerland to complete a graduate course at the Jean Jacques Rousseau Institute of Psychology at the University of Geneva.
While there she "fell in love with Europe" and set her heart on a career on the Continent. She applied to the state department but was told instead to brush up her secretarial skills (despite her avowedly old-fashioned values, such patronising attitudes ensured Baldrige "marched in the pro-feminist parade").
Having done so, she was appointed social secretary to David Bruce, the US ambassador to France, and his wife, Evangeline. After three "incredible" years she returned to America, where, by her own admission, she would litter conversation with Gallicisms and generally look down upon people.
"I was thoroughly obnoxious, a big blonde snob, really bad news," she said in a New York Times interview.
Soon, her language skills saw her posted to Rome, where she became secretary to Ambassador Clare Boothe Luce. On her return she moved to Tiffany as a director of public relations.
The call to join the Kennedy team came in July 1960, immediately after John F Kennedy had secured the Democratic presidential nomination.
Baldrige accepted despite being a registered Republican, and the following January she became an essential cog in a White House that was soon famous for balls and parties, cultural soirées and state dinners, all carried off with a previously unthinkable élan.
She remained at the heart of such events for three years, but in 1963 declared that she "had had it" with the long hours. She left before JFK's assassination, though she returned on a temporary basis to help his widow plan his funeral.
The following year she launched her own PR firm and by the 1970s she had established herself as a "doyenne of decorum" with a newspaper column and an update in 1978 of Amy Vanderbilt's Complete Book of Etiquette.
Such was her celebrity that, on November 27, 1978, she appeared on the cover of Time. She continued to work well into old age, relentlessly promoting each new tome, including a novel Public Affairs, Private Relations, a lightly fictionalised roman de moeurs featuring the First Lady and her very best friend.
Despite begin 6ft 1in and sporting an intimidatingly rigid silvery hairdo, Baldrige always said that she was simply advocating gentle good manners, not an inflexible rule book of behaviour.
This warm-hearted attitude was bolstered by her fondness for recounting the social disasters for which she herself had been to blame.
The catalogue of calamity began in June 1947, when she was invited through her father to attend a garden party at Buckingham Palace. It was crowded and, turning from one conversation she stretched out a leg over which a large figure tripped and was sent flying. It was Winston Churchill. "I wanted to die," she said.
In Paris she once seated a senior official from the French Foreign Ministry next to his wife's lover. "Everyone in France knew about the liaison except me," she said.
In Rome, Letitia Baldrige visited the city's catacombs with the ambassador's husband, Henry Luce, but, after a bout of claustrophobia, retreated, accidentally locking the door behind her on her way out. He was trapped for almost three hours.
While there she also introduced the new Pakistani ambassador as the envoy from India, which sent the diplomat storming from the room.
By her account, he refused her letters and calls of apology for three days until: "Finally, in desperation, I sent him a dozen red roses. He called me up and said: 'I cannot resist a young woman who sends me roses.' So if you really screw up, send roses."
She married Robert Hollensteiner in 1963. He survives her, with their daughter Clare and son Malcolm, who proved that even the offspring of models of manners were not necessarily exemplars of etiquette.
"He's always got the spoon in the ice cream carton, because he can't be bothered with a dish," Baldrige complained. "I think he really does it to twit me."
Letitia Baldrige, born on February 9, 1926, died on October 29, 2012.