Tributes are being paid to Neil Armstrong, the first man to walk on the moon, following his death, aged 82.
Armstrong underwent a heart-bypass surgery earlier this month, just two days after his birthday on August 5, to relieve blocked coronary arteries.
His family announced his death today (local time).
As commander of the Apollo 11 mission, Armstrong became the first human to set foot on the moon on July 20, 1969. As he stepped on the dusty surface, Armstrong said: "“That's one small step for (a) man, one giant leap for mankind."
Those words endure as one of the best known quotes in the English language.
Buzz Aldrin, his crew-mate on the Apollo 11 mission and the second man on the moon paid tribute to Armstrong today via Twitter.
"On behalf of the Aldrin family we extend our deepest condolences to Carol & the entire Armstrong family on Neil's passing. He will be missed."
US President Barack Obama also praised Armstrong following news of his death.
"Neil was among the greatest of American heroes - not just of his time, but of all time. When he and his fellow crew members lifted off aboard Apollo 11 in 1969, they carried with them the aspirations of an entire nation."
Michael Collins, who flew to the moon with Armstrong and served as the command module pilot said: ''He was the best, and I will miss him terribly.''
NASA chief Charles Bolden recalled Armstrong's grace and humility in a statement on Saturday. ''As long as there are history books, Neil Armstrong will be included in them, remembered for taking humankind's first small step on a world beyond our own."
A VERY PRIVATE MAN
Neil Alden Armstrong was 38 years old at the time of the landing and even though he had fulfilled one of mankind's quests that had loomed for centuries and placed him at the pinnacle of human achievement, he did not revel in his accomplishment.
He even seemed frustrated by the acclaim it brought.
"I guess we all like to be recognized not for one piece of fireworks but for the ledger of our daily work," Armstrong said in an interview on CBS's "60 Minutes" program in 2005.
He once was asked how he felt knowing his footprints would likely stay on the moon's surface for thousands of years. "I kind of hope that somebody goes up there one of these days and cleans them up," he said.
James Hansen, author of "First Man: The Life of Neil A. Armstrong," told CBS: "All of the attention that ... the public put on stepping down that ladder onto the surface itself, Neil never could really understand why there was so much focus on that."
The Apollo 11 moon mission turned out to be Armstrong's last space flight. The next year he was appointed to a desk job, being named NASA's deputy associate administrator for aeronautics in the office of advanced research and technology.
Armstrong's post-NASA life was a very private one. He took no major role in ceremonies marking the 25th anniversary of the moon landing. "He's a recluse's recluse," said Dave Garrett, a former NASA spokesman.
"Howard Hughes had nothing on him," he said, speaking of the reclusive aviator.
Hansen said stories of Armstrong dreaming of space exploration as a boy were apocryphal, although he was long dedicated to flight. "His life was about flying. His life was about piloting," Hansen said.
He left NASA a year after Apollo 11 to become a professor of engineering at the University of Cincinnati.
The former astronaut lived in the Cincinnati area with his wife, Carol.
"We are heartbroken to share the news that Neil Armstrong has passed away following complications resulting from cardiovascular procedures," the family said in a statement. "Neil was our loving husband, father, grandfather, brother and friend.
Facts about former US astronaut Neil Armstrong, the first man to walk on the moon, who has died at the age of 82:
* Armstrong grew up in Ohio with a strong interest in flight and earned his pilot's license while still a boy.
* After flying combat missions during the Korean War, he became a test pilot and joined NASA's astronaut program in 1962.
* As he stepped on the moon's dusty surface, Armstrong said: "“That's one small step for a man, one giant leap for mankind."
* Armstrong's pulse was measured at 150 beats per minute as he guided the lunar lander to the moon's surface, NASA said. Asked about his experience on the moon, he told CBS: "It's an interesting place to be. I recommend it."
* A crater on the moon is named for Armstrong. It is located about 30 miles (48 km) from the site of the landing.
* Armstrong took a NASA desk job after the Apollo 11 mission, becoming the deputy associate administrator for aeronautics in the office of advanced research and technology. A year later he became a professor of engineering at the University of Cincinnati.
* In 2005 Armstrong was upset to learn that his barber had sold clippings of his hair to a collector for $US3000. The man who bought the hair refused to return it, saying he was adding it to his collection of locks from Abraham Lincoln, Napoleon, Marilyn Monroe, Albert Einstein and others.
* Despite his taciturn nature, Armstrong once appeared in a television commercial for the US automaker Chrysler. He said he made the ad because of Chrysler's engineering history and his desire to help the company out of financial troubles.