Neil Armstrong had undergone heart surgery earlier this month (AP/Nasa)
Tributes have poured in from around the world to Neil Armstrong, the first man to walk on the Moon, who has died at the age of 82.
The former Nasa astronaut had suffered complications from heart surgery he underwent earlier this month, his family said.
He famously uttered the quote moments after setting foot on the lunar surface: "That's one small step for man, one giant leap for mankind."
US president Barack Obama tonight hailed Armstrong as one of America's greatest heroes. In a statement issued by the White House, Mr Obama said the crew of Apollo 11 carried with them the aspirations of an entire nation when they set out for the moon in 1969.
He later tweeted: "Neil Armstrong was a hero not just of his time, but of all time. Thank you, Neil, for showing us the power of one small step."
Astronomer Sir Patrick Moore said: "As the first man on the Moon, he broke all records. I knew him well. He was a man who had all the courage in the world." Physicist Professor Brian Cox tweeted: "Sad to hear about death of Neil Armstrong. I do think Apollo was the greatest of human achievements. For once, we reached beyond our grasp."
Armstrong commanded the Apollo 11 spacecraft that landed on the Moon on July 20 1969. He and fellow astronaut Edwin "Buzz" Aldrin spent nearly three hours walking on the Moon, collecting samples, conducting experiments and taking photographs.
Mike Cruise, professor of astrophysics and space research at the University of Birmingham, said: "The people at the front of the race always have to tread on new ground. He led the whole world into a space era of greater proportion than has been achieved by satellites. You wonder when his first steps will be followed up. It must have been very awe-inspiring to step on to, essentially, a new planet."
Jamie Burgess, from the UK National Space Centre, in Leicester, said: "I think it is safe to say (he was) a very brave man, a very courageous man. To be able to have that bravery is an incredible quality in a person. He is a fantastic character and will be sorely missed."
An estimated 600 million people - a fifth of the world's population - watched and listened to the first moon landing, the largest audience for any single event in history. The moonwalk marked America's victory in the Cold War space race that began on October 4 1957 with the launch of the Soviet Union's satellite Sputnik 1. Apollo 11 command module pilot Michael Collins, who was part of the historic moon-landing mission, paid tribute to Armstrong, his former colleague. He said: "He was the best, and I will miss him terribly."