Editor's note: John Glenn, a legendary NASA astronaut and American hero, died on Dec. 8, 2016 at age 95. Read our full obituary here.

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The first American to orbit the Earth, John Glenn made history again when, at the age of 77, he became the oldest person to travel in space. But before he was nationally recognized as a hero, he had put his life on the line for his country many times.

Born on July 18, 1921, in Cambridge, Ohio, John Herschel Glenn Jr., was the son of John and Teresa Sproat Glenn. While playing in the high school band, he met Anna Margaret Castor, and later married her. After graduation, he attended Muskingum College, where he attained a Bachelor of Science degree in Engineering. Following the Japanese attack on Pearl Harbor, Glenn entered the Naval Aviation Cadet Program. He ultimately flew 59 combat missions in the Pacific during World War II.

Astronaut John Glenn photographed in space by an automatic sequence motion picture camera during his historic orbital flight on "Friendship 7" on Feb. 20, 1962. (Image credit: NASA)

After the war ended, Glenn served as an instructor for advanced flight training at Corpus Christi, Texas. He went on to fly 90 missions in Korea, downing three MiGs during the his last nine days of combat.

From there, Glenn attended Test Pilot School at the Naval Air Test Center in Maryland, then went on to serve as project officer on a number of aircraft. He attended classes at the University of Maryland for two and a half years while assigned to the Fighter Design Branch of the Navy Bureau of Aeronautics, the precursor to the Bureau of Naval Weapons.

In July 1957, Glenn set a transcontinental speed record, flying from Los Angeles to New York in 3 hours 23 minutes. His was the first cross-country flight to average supersonic speed.

Glenn was awarded the Distinguished Flying Cross six times, as well as a number of other honors for his military service. He and his wife have two children.

Beyond the sky

In April 1959, Glenn was selected as a Project Mercury astronaut. He became part of the Mercury Seven group, the first astronauts selected by NASA. Glenn served as backup astronaut to the first two Americans in space, Alan Shepard and Virgil "Gus" Grissom. [Project Mercury: Photos of NASA's 1st Manned Spaceflights]

At the time, the United States was in the midst of a race with the Soviet Union to reach the stars. Russian astronaut Yuri Gagarin became the first man launched into space on April 12, 1961, beating Alan Shepard by less than a month. Gagarin's craft took him in a full orbit around Earth, making him the first person to circle the planet, as well. [Infographic: 1st American in Orbit: How NASA & John Glenn Made History]

On Feb. 20, 1962, the United States showed that it had the same mettle as its competition. Previous flights into space by Shepard and Grissom had not traveled all the way around the planet. When Glenn blasted into space aboard Mercury's Friendship 7 capsule, he orbited Earth three times over the course of almost five hours, traveling faster than 17,000 mph. [VIDEO: This is Friendship 7: America's 50th On-Orbit Anniversary]

But his journey was not without hazards. After the first orbit, a mechanical problem with the automatic control system required Glenn take manual control of the craft. Sensors also indicated that the heat shield, which would protect the astronaut from the lethal temperatures created upon re-entry to the atmosphere, was loose. To help protect him on his return to Earth, Glenn kept the retrorocket pack, which was designed to be jettisoned, in place. Follow-up examination of the control system revealed that the indicator had been incorrect. The shield was fine, but the experience was surely harrowing. [PHOTOS: John Glenn, First American in Orbit]

An active retirement

Glenn retired from the Marine Corps in 1965 as a colonel. He worked as a business executive for a decade before being elected to the U.S. Senate in 1974. The Ohio Democrat campaigned vigorously for funding for science, education, and space exploration. In 1984, he made a failed bid for the Democratic presidential nomination. He served as a senator until 1999.

STS-95 crewmember, astronaut and U.S. Senator John Glenn. Glenn was the first American to orbit the earth and returned to space in 1998 aboard a Space Shuttle flight. (Image credit: NASA/Robert Markowitz, Mark Sowa)

Despite his advancing age, Glenn was not yet finished with the space program. On Oct. 29, 1998, while still a senator, Glenn made history again when he rode the space shuttle Discovery to become the oldest space traveler. Over the course of nine days, the shuttle orbited Earth 134 times.

Glenn served as payload specialist, participating in various experiments to test how his 77-year old body responded the weightless environment. The craft also carried the SPARTAN satellite to study solar wind, and hardware for an upcoming maintenance mission on the Hubble Space Telescope.

In 2012, Glenn received the Presidential Medal of Freedom. He was also on hand for the retirement of the space shuttle Discovery, though he criticized the demise of the shuttle program as delaying research.

Although Glenn's second flight into space was completely different from his first, both were historic, record-setting missions. But most Americans will always remember him as the first American to orbit the Earth.

—Nola Taylor Redd