Designer Oleg Cassini is largely responsible for Jackie Kennedy's prolific status in the fashion world today. With his European-inspired coats and suits, Cassini reportedly designed 300 outfits for Kennedy in less than three years, according to L'Officiel. One of his most notable designs was a leopard coat spotted on the first lady in 1962. The piece skyrocketed in demand so aggressively that over 250,000 leopards were killed to help fulfill sales, prompting Cassini to vow to never work with real fur again, according to CR Fashion Book.

But perhaps the Cassini-Kennedy collaboration that most strongly sits with the memory of the American fashion zeitgeist is when she wore one of his coats to her husband's inauguration. The beige wool coat came with a straight-lined silhouette and a distinct row of buttons, garnering much public attention and creating a precedent during the 1960s, per Insider.

Kennedy also popularized collarbone action through her repeated wearing of strapless gowns. From a baby pink Christian Dior dress at the White House in 1962 (via TIME), to an elegant lavender evening gown in 1963 at The National Gallery of Art, she set the trend for one of the most prevalent silhouettes in her era.