No further information on Glenn's cause of death was available.
"John Glenn is the last of the original seven American astronauts who truly had the 'right stuff.' On top of paving the way for the rest of us, he was also a first-class gentleman and an unabashed patriot," U.S. Sen. Bill Nelson, a Florida Democrat, said in a statement.
Glenn's 4-hour, 55-minute spaceflight on Feb. 20, 1962 marked a turning point in the tense race with the Soviet Union to develop missiles capable of precision strikes across the continents. Space was where the technology was showcased and until Glenn's flight, America was behind.
The Soviets had launched the first satellite, Sputnik, on Oct. 4, 1957, the first animal (a dog named Laika) on Nov. 3, 1957, and then the first person, cosmonaut Yuri Gagarin, on April 12, 1961.
"Sputnik was totally unexpected," historian Alan Marcus, now with Mississippi State University, said in an interview marking the 40th anniversary of Glenn's flight.
"Here were what we thought were these backward Russians putting up a satellite. Then came the Cuban missile crisis and we had this incredible tension between the Soviet Union and us. All these problems made Glenn's flight rewarding, but it was not the end-all be-all … It was a step on the way to winning the Cold War," he said.
Against that backdrop came Glenn, a straight-laced Marine Corps pilot from Ohio who had flown 59 combat missions during World War II and 100 missions in Korea before being selected as one of NASA's first astronauts.
In addition to Shepard, Grissom and Glenn, the Mercury Seven included Scott Carpenter, Gordon Cooper, Wally Schirra and Deke Slayton. Glenn, the eldest of the group, was the last surviving member.
Glenn made three orbits around Earth, reaching a maximum altitude of about 162 miles and a speed of about 17,500 mph before splashing down 800 miles southeast of Cape Canaveral, Florida, near Grand Turk Island. He returned home an instant hero, honored with a ticker-tape parade in New York City and a Congressional Medal of Honor from President Kennedy.
Read more at Discovery News