Do any research into sexual activity and you typically come across the names Masters and Johnson. But just who are these people?

William Masters and Virginia Johnson revolutionized the way sex is studied, taught and enjoyed in America. The two are often referred to as the most famous sexologists of their day.

Masters, an obstetrician and gynecologist born in 1915, became interested in human sexuality because he considered it the last scientifically unexplored physiological function. In 1947 he joined the faculty at Washington University in St. Louis. He conducted field research and wrote dozens of scientific papers.

Johnson was born in 1925. She worked in insurance for several years, but also studied piano and voice. Her politician mother had Johnson sing for elected officials at various meetings. Those performances led to a short-lived stint as a country music singer. In the mid 1950s, she began studying for a social anthropology degree at Washington University.

The two met in 1957 when Masters hired Johnson as a research assistant and they performed some of the most daring and controversial experiments in the history of sexual research.

Their initial study was conducted with 382 women and 312 men participating. Masters and Johnson observed and measured sexual behavior as the volunteers masturbated, fondled each other, performed oral sex and anal sex and had intercourse. For the first time, researchers cited female sexual response as consisting of four phases: excitement, plateau, orgasm and resolution.

In 1966, they published their findings in their book, Human Sexual Response. Although the book was written in dry, clinical terms, its provocative subject matter made it a best seller.

In their second book, Human Sexual Inadequacy, the two discussed issues such as impotence and other problems in sexual performance.

Masters divorced his first wife and married Johnson in 1971. Two years later, they became co-directors of the Masters and Johnson Institute.

In 1979, Masters and Johnson studied the sexual responses of homosexuals and lesbians in Homosexuality in Perspective. Their 1988 book, Crisis: Heterosexual Behavior in the Age of AIDS predicted an epidemic of AIDS among heterosexuals, causing many in the medical community to condemn the study.

Masters and Johnson divorced after 21 years of marriage due to differences relating to work and retirement. Masters died in Tucson, Ariz. at age 85. He suffered complications from Parkinson's disease. As of this writing, Johnson still lives in St. Louis.

Stacy Lloyd is a writer and video producer in Phoenix, Arizona. A former television news journalist, she covered stories around the world. Currently, she produces corporate and non-profit videos and broadcast programming.