Mainbocher (born Main Rousseau Bocher) was an American couturier who operated fashion houses in Paris and later New York from the 1930s through the 1960s. He is best known for designing Wallis Simpson's wedding dress and trousseau for her 1937 marriage to the former Edward VIII (the Duke of Windsor) which was photographed by Cecil Beaton.

Mainbocher was a native of Chicago, where he studied art at the University of Chicago and the Chicago Academy of Fine Arts. He served in the Army in the first World War and stayed on in Paris after the war, working as a fashion illustrator for Harpers Bazaar and later as a fashion editor for French Vogue.

In 1929, he established his own fashion house, designing expensive, elegant haute couture dresses and gowns for an exclusive clientele, and charging them for the privilege of viewing his collections. He designed much of the Duchess of Windsor's wardrobe, naming a color, Wallis blue, for her, and created the first strapless evening gown.

In 1939 , he relocated his business to New York on 57th Street next to Tiffany's, and continued to design for generations of discerning women of means like Gloria Vanderbilt through the 1960s.

After he achieved fame for dressing some of the world's most famous women, Mainbocher was commissioned to design the costumes for Mary Martin in the 1943 Broadway musical One Touch of Venus and for Ethel Merman in the 1950 musical Call Me Madam.

Mainbocher and twenty-three other American fashion designers were honored with bronze plaques on New York City's "Fashion Walk of Fame" in the legendary garment district.