A graduate of the United States Naval Academy at Annapolis, Shepard saw action with the surface navy during World War II. He became a naval aviator in 1946, and a test pilot in 1950. He was selected as one of the original NASA Mercury Seven astronauts in 1959, and in May 1961 he made the first manned Project Mercury flight, MR-3, in a spacecraft he named Freedom 7.
He became the second person, and the first American, to travel into space, and the first person to manually control the orientation of his spacecraft.
He was Chief of the Astronaut Office from November 1963 to July 1969 (the approximate period of his grounding), and from June 1971 until his retirement from the United States Navy and NASA on August 1, 1974. He was promoted to rear admiral on August 25, 1971, the first astronaut to reach that rank.
According to Wikipedia