That honor, as an American, would go to John Glenn on February 20, 1962.
The original 7 included Shephard, Scott Carpenter, Gordo Cooper, John Glenn, Gus Grissom, Wally Schirra, and Deke Slayton.
Future historians will note this period as a turning point in human history.
Project Mercury had 3 primary objectives:
To orbit a manned spacecraft around Earth
To investigate man's ability to function in space
To recover both man and spacecraft safely