Los Angeles ? Gordon Cooper, who was the youngest and perhaps cockiest member of the original Mercury astronauts and set the space endurance record that helped clear the way for the first moon landing, has died. He was 77.

Cooper died Monday at his home in Ventura, NASA officials said in a statement. He died of natural causes, said Mitch Breese, of the county medical examiner’s office.

“As one of the original seven Mercury astronauts, Gordon Cooper was one of the faces of America’s fledgling space program,” said NASA Administrator Sean O’Keefe. “He truly portrayed the right stuff, and he helped gain the backing and enthusiasm of the American public, so critical for the spirit of exploration.”

As one of the nation’s first astronauts, Cooper became a hero to a generation of Americans in the early 1960s as the country tried to catch the Soviet Union in the space race.

On May 15, 1963, Cooper piloted Faith 7, the Mercury program’s last flight, circling the globe 22 times in 34 hours and 20 minutes. The mission made him the last astronaut to orbit Earth alone and the first to take a nap during the journey.

Cooper became the first man to make a second orbital flight two years later during the Gemini 5 mission, when he and Charles Conrad established a space endurance record by traveling more than 3.3 million miles in 190 hours, 56 minutes.

The flight proved humans could survive in a weightless state for the length of a trip to the moon and tested a new power source for future flights — fuel cells. It also let the United States take the lead in the space race by surpassing the Soviet Union in man-hours in orbit.

Cooper’s rambunctious attitude was immortalized in Tom Wolfe’s book “The Right Stuff” and the 1983 movie of the same name. Dennis Quaid portrayed Cooper in the movie.

Cooper gave his signature line during a 1995 reunion of surviving Mercury astronauts. When asked who was the greatest fighter pilot he ever saw, Cooper enthusiastically answered, “You’re looking at him!”

Astronaut Gordon Cooper is shown in his space suit in this July 1965 file photo. Cooper, one of the original Mercury astronauts who were pioneers in human space exploration, died Monday at age 77.

“Gordon Cooper’s legacy is permanently woven into the fabric of the Kennedy Space Center as a Mercury Seven astronaut,” said center director Jim Kennedy. “His achievements helped build the foundation of success for human space flight that NASA and KSC have benefited from for the past four decades.”

Cooper’s death came the day that privately built SpaceShipOne broke through the Earth’s atmosphere for the second time in five days, capturing a $10 million prize aimed at opening the final frontier to tourists.

Three of the original Mercury astronauts are still alive — John Glenn, Scott Carpenter and Wally Schirra.

Virgil “Gus” Grissom died in the 1967 Apollo 1 fire; Donald K. “Deke” Slayton died of brain cancer in 1993; and Alan Shepard Jr., died of leukemia in 1998.