Cooper, a former Air Force colonel, piloted the sixth and final flight of the Mercury program -- the first US manned space flight -- and later commanded Gemini V.

The May 15-16, 1963 manned space flight lasted more than 34 hours and 22 orbits around the Earth -- more than three times the longest manned American space flight until then, and far beyond the initial design capability of the capsule. That mission also made him the first person to sleep in space.

"As one of the original seven Mercury astronauts, Gordon Cooper was one of the faces of America's fledgling space program," NASA Administrator Sean O'Keefe said in a statement.

Cooper "truly portrayed the right stuff, and he helped gain the backing and enthusiasm of the American public, so critical for the spirit of exploration."

Cooper and his fellow astronauts, known as the "Mercury Seven," -- Alan Shepard, Gus Grissom, John Glenn, Scott Carpenter, Wally Schirra and Deke Slayton -- were immortalized in the Tom Wolfe bestseller "The Right Stuff."

The book was turned into a blockbuster Hollywood movie in 1983, in which actor Dennis Quaid played the young, hot-shot pilot Cooper.

Leroy Gordon Cooper Jr was born in Shawnee, Oklahoma, in 1927. He served in the Marine Corps and then went to the University of Hawaii.

He received a commission as a second lieutenant in the Army, and then from 1950 to 1954 was an Air Force fighter pilot in Germany.

He completed his university studies at the Air Force Institute of Technology, and then trained to become a test pilot at Edwards Air Force Base in California.

Cooper kept working as a test pilot until he was picked to become an astronaut as the youngest man on the Mercury team.

After the landmark 1963 flight, he and astronaut Charles Conrad flew an eight-day mission that, despite many problems, helped prove to the National Aeronautics and Space Administration that a mission to the moon was possible.

Cooper retired in 1970, but continued to work in a number of industries, including helping Walt Disney Productions with its futuristic Epcot theme park at DisneyWorld in Orlando, Florida.

He is survived by his wife, Susan, and two daughters. NASA did not reveal the cause of Cooper's death.

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