NEW YORK — For nearly all his 91 years, fashion designer Oleg Cassini has been on the move. There’s little chance his pace will slow anytime soon. He became first lady Jacqueline Kennedy’s official couturier in 1961 and made the pillbox hat internationally known. Before that, the Parisian-born, Italian-educated count ranked as a tennis pro and served in the U.S. Army. He built his fashion career in Europe, Hollywood and New York. “I’m doing things the way I’ve been doing them,” Cassini says. “Most men that I compete against put a stop to their career when they become typical.” His advice: “Be mobile at all times, even if it causes you suffering, or feelings of loneliness. Unless you’re willing to do that, you’re never going to get the bigger rewards.” During a recent interview at the mansion that serves as his headquarters, Cassini recounted highlights of what is perhaps history’s longest fashion career and

celebrity lifestyle that involved dressing famous women, including Kennedy, one-time fiancé Grace Kelly and Marilyn Monroe.

“Oleg Cassini’s name is probably one of the most recognized fashion names globally,” says Lavelle Olexa, a senior vice president at Lord & Taylor. “The thing that always makes him so important is that he’s always relevant. I think that, too, is the way he lives his life … he personifies living in the now and looking to tomorrow.”

Cassini unveils his New Couture Resort Jeans Collection later this month at Lord & Taylor. The retailer also plans to honor the 50th anniversary of Cassini’s first window display at its flagship Fifth Avenue department store.

“Why would people be interested in me now? I think I have talent,” Cassini says. “I kept it.”

Then he adds, “It’s my extreme modesty.”

Yet for all his successes, Cassini manages to retain some humility, crediting the glamorous women he counted among his clients and friends. “I would’ve had to be pretty clumsy not to have done something with it,” he says.

Arguably the first “celebrity designer,” Cassini pioneered looks through the 1950s and ‘60s, such as the A-line dress and colored dress shirts for men, which remain popular to this day. He also employed the idea of licensing, extending the Cassini brand to beauty care products, fragrances and even a custom-designed automobile interior in the 1970s.

In the ‘90s, Cassini launched a partnership with David’s Bridal.

Robert Huth, president and CEO of May Department Stores’s bridal group, predicts subsidiary David’s Bridal could sell upward of 45,000 Cassini dresses this year. The company also plans to expand the line into Europe.

“He will clearly be one of the largest lines in the U.S., if not the largest bridal designer,” Huth says, adding that Cassini enjoys a high degree of name recognition among mothers of brides. “He is quite an icon in the design industry, particularly because of Jackie Kennedy and others.”

Born in Paris after his family fled the Russian Revolution, Cassini earned his doctorate in fine arts in Italy, worked for the Patou fashion house in Paris and in 1933 launched his own design studio before heading across the Atlantic.

“It was impossible to find a job,” Cassini says, explaining how he arrived amid the Great Depression. “You could survive on 15 cents a day, which I did.”

Hollywood soon beckoned and Cassini quickly landed a position at Paramount Studios, where he dressed some of the top movie stars during the 1940s. But sensing that the big studio system had seen better days, Cassini moved to New York in the 1950s and launched his business on Seventh Avenue, the epicenter of American fashion.

Cassini recalls his first New York clothing line: “I had a really good collection, probably the best I did in my whole life.”

Apparently, Lord & Taylor liked it, too; it featured the line – striking for its bold buttons, minimalist sleeves and shapely skirts – in its window displays.

The exposure led to an invitation to visit with Kennedy, who asked Cassini if he would like to design a piece or two for her.

“I took a chance,” Cassini says. “I said no.”

Cassini told her that inviting designers to contribute to her wardrobe would cause “everybody to fight like dogs for your attention, for your time.” Cassini argued that choosing a single couturier would serve her better in the long run.

“She said, ‘You convinced me. You’re the one,’ ” he recalls.

Cassini believes it was such a successful partnership because he understood both Kennedy’s figure and taste. “A designer understands what she should wear, not what she thinks she should wear,” he says. “I was successful because I listened.”

Sometimes their partnership worked too well: Asked by Kennedy for a fur coat recommendation, Cassini replied, “Leopard.” The ensuing popularity of exotic cats’ pelts led to a sharp rise in demand.

“Two-hundred-fifty thousand leopards were killed,” Cassini says. “I regret it.”

Cassini’s love of animals prompted him to adopt 32 cats, 10 dogs, two miniature horses, three racehorses, three Vietnamese potbellied pigs and 16 ducks, most of which live at his estate in Oyster Bay, N.Y., that was previously owned by the Tiffany family. He splits his time between there and his 17th-century townhouse in Manhattan’s Gramercy Park neighborhood. He travels with one dog, a miniature poodle named Rambo.

At 80, Cassini decided he would try his hand at harness horse racing – a pastime he gave up only a couple of years ago because of concerns over the dangers.

“I have sections of things in my life to make it more exciting,” he says.

Pointing to a photograph in his office of himself in his color-coordinated jockey’s uniform he says inspired his designs at the time, Cassini adds, “I got some very nice sportswear out of it.”

Cassini maintains he has “programmed” himself for longevity.

“Half a century has passed and here I am,” he says. “I have 15 to 20 years left – at least.”