US President Barack Obama and astronaut Buzz Aldrin led tributes to the Apollo 11 commander Neil Armstrong, the first man on the moon, lauding him as a reluctant but true American hero.
Armstrong, who died aged 82 from complications following cardiac bypass surgery, was praised for his willingness to embrace and conquer challenges that once seemed impossible.
"When he and his fellow crew members lifted off aboard Apollo 11 in 1969, they carried with them the aspirations of an entire nation," Obama said.
"When Neil stepped foot on the surface of the moon for the first time, he delivered a moment of human achievement that will never be forgotten."
Aldrin, who with Armstrong was watched by an estimated global television audience of 500 million as they bounced on the moon's surface in their chunky spacesuits, praised his comrade's skill, dedication and selflessness.
"I know I am joined by millions of others in mourning the passing of a true American hero and the best pilot I ever knew," Aldrin said. "I will miss my friend Neil as I know our fellow citizens and people around the world will miss this foremost aviation and space pioneer."
The third Apollo 11 astronaut - Michael Collins, the command module pilot who orbited the moon while his crewmates landed - said Armstrong "was the best, and I will miss him terribly."
Armstrong and Aldrin landed on the moon on July 20, 1969. His first words upon stepping on the desolate lunar surface have since been etched in history: "That's one small step for (a) man, one giant leap for mankind."
Armstrong, a Korean war veteran who was decorated by 17 countries and received a slew of US honours, was never comfortable with the worldwide fame that stemmed from the Apollo 11 mission, and he shied away from the limelight.
John Glenn, the first American to orbit earth, recalled Armstrong's legendary humility.
"He didn't feel that he should be out huckstering himself," the former Ohio senator told CNN. "He was a humble person, and that's the way he remained."
Born in Wapakoneta, Ohio on August 5, 1930, Armstrong took flying lessons at the age of 15 and received his pilot's licence on his 16th birthday.
A US Navy aviator, he later joined Nasa's predecessor agency, the National Advisory Committee for Aeronautics, in 1955. As a research pilot at Nasa's Flight Research Centre in Edwards, California, he flew on many pioneering high-speed aircraft.
In 1962, as command pilot for the Gemini 8 mission, he performed the first successful docking of two vehicles in space.