Katherine Sophie Dreier (September 10, 1877 – March 29, 1952) was an American artist, lecturer, patron of the arts and social reformer. Dreier developed in interest in art at a young age and was afforded the opportunity of studying art in the United States and in Europe due to her parents' wealth and progressive attitudes. Her sister Dorothea, a Post-Impressionist painter traveled and studied with her in Europe. She was most influenced by modern art, particularly by her friend Marcel Duchamp, and due to her frustration with the poor reception that the works received, she became a supporter of other artists. She was co-founder of the Society of Independent Artists and the Société Anonyme, which had the first permanent collection of modern art, representing 175 artists and more than 800 works of art. The collection was donated to Yale University. Her works were exhibited in Europe and the United States, including the 1913 International Exhibition of Modern Art.
Dreier was also an active suffragette, attending the sixth convention of the International Woman Suffrage Alliance in Stockholm, Sweden as a delegate. She was the head of the New York City's German-American Committee of the Woman Suffrage party in 1915 and treasurer of the organization her mother established, German House for Recreation of Women and Children. She co-founded the German House for Recreation of Women and Children, and was its president. Two of her sisters were social reformers, Mary Dreier and Margaret Dreier Robins.