William Howell Masters (December 27, 1915 – February 16, 2001) was an American gynecologist. He was best known as the senior member of the Masters and Johnson sexuality research team. With Virginia Johnson, he did research into the nature of human sex. The work lasted from 1957 until the 1990s. It included the diagnosis and treatment of sexual disorders and dysfunctions. This was a more orthodox kind of research than that done by Alfred Kinsey.