Cassini's name was nearly synonymous with that of Jacqueline Kennedy - creating the dresses that helped make the first lady a trend-setter.
Kennedy, only 31 when her husband was elected president, was the pinnacle of style in the White House years from 1961 to 1963. Her simple, geometric dresses in sumptuous fabrics, her pillbox hats and her elegant coiffure were copied by women from 18 to 80.
Cassini said that shortly after John Kennedy was elected, he persuaded his wife that she should use him as the creator of her total look, rather than one of many designers. The one-time Hollywood costume designer turned couturier had been friendly with the Kennedy family for years.
"We are on the threshold of a new American elegance thanks to Mrs. Kennedy's beauty, naturalness, understatement, exposure and symbolism," Cassini said when his selection was announced.
The fashion establishment was shocked, Women's Wear Daily journalist John Fairchild wrote in his 1965 book "The Fashionable Savages."
"Everyone was surprised," he wrote. "Oleg Cassini had been around for years. He was debonair, amusing, social, but none of the fashion intellectuals had considered him an important designer."
Cassini was born in 1913 in Paris to wealthy, aristocratic Russian parents who were later forced to flee their homeland after the Revolution. They settled in Italy, their fortune gone, but his mother gained some success as a dressmaker and her son eventually decided to go into the fashion business, too.
He came to the United States in 1936 and held various design jobs in New York before going to Hollywood and landing a job at Paramount in the early 1940s.
With the fame that came with his White House assignment came new business opportunities. He was one of the first designers to pursue licensing agreements that put his name on a large variety of products from luggage to nail polish.