John Herschel Glenn Jr. (born July 18, 1921) is a retired United States Marine Corps pilot, a former astronaut and United States Senator who was the first American and third person to orbit the Earth. Glenn was a Marine Corps fighter pilot before joining NASA's Mercury program, NASA's original astronaut group. He orbited the Earth on Friendship 7 in 1962. After retiring from NASA, he entered politics as a Democrat and represented Ohio in the United States Senate from 1974 to 1999.

Glenn received a Congressional Space Medal of Honor in 1978 and was inducted into the Astronauts Hall of Fame in 1990. In 1998, he became the oldest person to fly in space, and the only one to fly in both the Mercury and Shuttle programs, when at age 77, he flew on the Space Shuttle Discovery (STS-95). Glenn and M. Scott Carpenter are the last surviving members of the Mercury Seven.

John Glenn was born in Cambridge, Ohio, to John Herschel Glenn and his wife Clara Sproat. He was raised in New Concord, Ohio. Glenn studied chemistry at Muskingum College, and received his private pilot's license as physics course credit in 1941. When the Attack on Pearl Harbor brought the United States into World War II, he dropped out of college and enlisted in the U.S. Army Air Corps. However, the Army did not call him up, and in March 1942 he enlisted as a United States Navy aviation cadet. He trained at Naval Air Station Olathe, where he made his first solo flight in a military aircraft. In 1943, during advanced training at the Naval Air Station Corpus Christi, he was reassigned to the United States Marine Corps. After completing his training, Glenn was assigned to Marine squadron VMJ-353, flying R4D transport planes. He eventually managed a transfer to VMF-155 as an F4U Corsair pilot, and flew 59 combat missions in the South Pacific. He saw action over the Marshall Islands, where he attacked anti-aircraft batteries and dropped bombs on Maloelap. In 1945, he was assigned to Naval Air Station Patuxent River, Maryland, where he was promoted to captain shortly before the war ended.