When Christian Dior introduced his New Look in 1947, it was not the product of decades in the trenches as a fashion designer. Rather, Dior’s famous postwar collection marked his professional debut.

Which is not to say that the collection was purely a case of beginner’s luck. Dior had been in the Paris fashion world for years, including productive stints as assistants to Robert Piguet and Lucien Lélong. By the time he opened his own couture house in 1946, he was already 41 years old.

Dior called his first collection Corolle, which was French for flower petals. Indeed, compared to the boxy, utilitarian, World War II fashions that had dominated the 1940s, Dior’s collection was a bouquet of bounty, with yards upon yards of fabric lavished on just one dress. The fashion press was smitten, with “Harper’s Bazaar” being the first to call it the New Look.

In fact, there was much that was not new at all about Dior’s breakthrough. Some have detected 1860s French influences, while Dior himself said that the collection reminded him of the clothes his mother had worn to the races when he was a young boy.

Though the fashion press fawned over Dior (“Vogue” covered him obsessively until his death in 1957), many Europeans were shocked by the excessive use of material at a time when fabric was still being rationed. Others resented the ornamentation of women—fellow Parisian Coco Chanel dismissed Dior’s look as the equivalent of dressing women up like armchairs.

Perhaps in deference to his critics, Dior’s subsequent collections were more pared down. For example, his A-line dresses, whose silhouette resembled the letter A, were signatures of the casual, unfussy 1950s.

After Dior’s death, Yves Saint Laurent, who had been a design assistant with the firm, was named chief designer, even though he was only 21. Within two years Marc Bohan had replaced Saint Laurent, and he stayed at that post for 28 years, longer than Dior himself had been at the helm of his own company...