William H. Masters was an American gynecologist and sexologist, best known for his pioneering research in human sexuality. Along with his research partner, Virginia E. Johnson, he co-authored the influential book, Human Sexual Response, which detailed the physiological responses of individuals during sexual activity. Their work laid the foundation for modern sex therapy and education. Masters and Johnson established the Masters and Johnson Institute in the 1960s, where they conducted clinical research and therapy sessions. Their studies challenged societal norms about sexuality and contributed significantly to the understanding of sexual dysfunction and intimacy, making a lasting impact on the field of sexual health.