US President Barack Obama has led tributes to astronaut Neil Armstrong, the first man on the moon, who died at the age of 82.
Mr Obama said on his Twitter feed: "Neil Armstrong was a hero not just of his time, but of all time."
Mr Obama thanked him for showing the world "the power of one small step".
Mr Armstrong, 82, underwent heart-bypass surgery two days after his birthday on 5 August to relieve blocked coronary arteries.
As commander of the Apollo 11 mission, he was the first human to set foot on the moon on 20 July, 1969.
"That's one small step for a man, one giant leap for mankind," Mr Armstrong said as he stepped on the moon's surface.
More than 500 million watched every moment of Apollo 11's arrival on the lunar surface. From inside the capsule, he reported to Mission Control in Houston that "the Eagle has landed".
He and 'Buzz' Aldrin spent nearly three hours walking on the moon.
Back on Earth, Mr Armstrong, Mr Aldrin and Michael Collins received global adulation and honour, and were feted like movie stars wherever they went.
Many of Mr Armstrong's colleagues and friends paid tribute to him as a modest, private man who never sought the limelight reports the BBC.
Mr Collins said: "He was the best, and I will miss him terribly."
Mr Armstrong was awarded the Presidential Medal of Freedom. But, after the initial publicity round, he refused to give interviews or sign autographs.
"I don't want to be a living memorial," he once said and was happy to "bask in obscurity".
The Apollo 11 moon mission was his last space flight. He left NASA in 1971 to become a professor of engineering at the University of Cincinnati.
The former astronaut lived in the Cincinnati area with his wife, Carol.
Complications from surgery
A statement by Mr Armstrong's family issued on Saturday said he died following complications resulting from the surgery.
Born in 1930 and raised in Ohio, Neil Armstrong took his first flight aged six with his father and formed a lifelong passion for flying.
His hero was Charles Lindbergh, and by the age of 16 he could fly before he could drive.
He flew Navy fighter jets during the Korean War in the 1950s, before joining the US space programme in 1962.
A crater on the moon is named after Neil Armstrong. It is located about 48 km from the site of the landing.
Last November, he and three other astronauts received the Congressional Gold Medal, the highest civilian award in the United States.
No one has walked on the moon since 1972.
Flags still flying
Apollo missions to the Moon ran from 1969 - 1972 and six flags were planted during this time.
NASA said in July that photos from a lunar spacecraft showed five of the flags are still standing.