Tributes have poured in for Neil Armstrong, the first man to walk on the moon, who died last night aged 82.
Armstrong's family said he died from cardiovascular surgery complications following a heart bypass earlier this month, Sky News reports.
They said they were "heartbroken", and called Armstrong "a reluctant American hero who always believed he was just doing his job."
US President Barack Obama hailed Armstrong as a "great American hero."
Buzz Aldrin, who walked on the moon's surface with Armstrong, tweeted: "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."
Astronomer 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."
NASA was also quick to express its sympathies, tweeting: "NASA offers its condolences on today's passing of Neil Armstrong, former test pilot, astronaut, & the 1st man on the moon."
Armstrong was commander of the Apollo 11 mission. He became the first man to set foot on the moon on 20 July, 1969. Nearly half a billion people tuned in to watch the historic event, and to hear Armstrong utter the famous phrase: "That's one small step for man, one giant leap for mankind."
The moonwalk marked America's victory in the space race against the Soviet Union. It was Armstrong's last space flight, as the following year he was appointed a desk job at NASA.
He didn't buy into the celebrity side of his career, making few public appearances, declaring: "I take a substantial amount of pride in the accomplishments of my profession."
Of walking on the moon, Armstrong once said: "The sights were simply magnificent, beyond any visual experience that I had ever been exposed to."