The first group of astronauts selected by NASA in 1959. The term began to be used after other groups were chosen. The seven astronauts were, from the US Air Force, Gordon Cooper Jr, Gus Grissom, and Deke Slayton; from the US Navy, Scott Carpenter, Walter Schirra Jr, and Alan Shepard Jr; and from the US Marines, John Glenn Jr.

They were chosen from 32 finalist candidates selected to take physical examinations. The original criteria required applicants to be less than 40 years old, less than 5 ft 11 in tall, in excellent physical condition, holding a bachelor's degree or equivalent, a graduate of a test pilot school and a qualified jet pilot, and to have logged at least 1 500 hours of flying time.

http://history.nasa.gov/40thmerc7/intro.htm Absorbing biographies of the ‘Original Seven’ astronauts. The site includes an image gallery, a chronology of events, links, and downloadable copies of contemporary documents.