Tributes have been paid to Neil Armstrong, the first man to walk on the moon, who has died at the age of 82.
The former Nasa astronaut underwent heart surgery earlier this month.
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."
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."
A statement from Mr Armstrong's family said he died following complications resulting from cardiovascular procedures.
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."
Former astronaut Tom Jones, who completed four space shuttle flights between 1990 and 2001, told Sky News: "Mr Armstrong was one of the astronauts that was my hero when I was growing up and I watched his initial landing on the moon in 1969 with incredible interest.
"I wanted to do exactly what Neil, and Buzz [Aldrin], and Mike Collins were doing that time. I hoped that one day I would have the chance to participate in the space programme.
"He really was an inspiration to an entire generation of people."
Mr Jones said meeting Mr Armstrong had been a "dream come true" and described being "star struck" by the chance to meet and work with his idol.
"He's a very unassuming and friendly person when you get to know him in a professional setting," he added.
Jamie Burgess, from the National Space Centre, 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.
Announcing his death, Mr Armstrong's family said in a statement: "We are heartbroken to share the news that Neil Armstrong has passed away following complications resulting from cardiovascular procedures.
"Neil was our loving husband, father, grandfather, brother and friend.
"Neil Armstrong was also a reluctant American hero who always believed he was just doing his job.
"He served his nation proudly as a Navy fighter pilot, test pilot, and astronaut.
"While we mourn the loss of a very good man we also celebrate his remarkable life and hope that it serves as an example to young people around the world to work hard to make their dreams come true, to be willing to explore and push the limits, and to selflessly serve a cause greater than themselves."
Physicist Professor Brian Cox later 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's family statement continued: "For those who may ask what they can do to honour Neil, we have a simple request. Honour his example of service, accomplishment and modesty, and the next time you walk outside on a clear night and see the moon smiling down at you, think of Neil Armstrong and give him a wink."
Apollo 11 command module pilot Michael Collins, who was part of the historic moon-landing mission, paid tribute to his former colleague.
Mr Collins said: "He was the best, and I will miss him terribly."
Mr Armstrong was born in Wapakoneta, Ohio, on August 5 1930, and would later begin his Nasa career in his home state.
After serving as a naval aviator from 1949 to 1952, he joined the National Advisory Committee for Aeronautics (NACA) in 1955.
Over the next 17 years, he worked as an engineer, test pilot, astronaut and administrator for NACA and its successor agency, the National Aeronautics and Space Administration (Nasa).
He transferred to astronaut status in 1962 and was assigned as command pilot for the Gemini 8 mission.
Gemini 8 was launched on March 16 1966, and Mr Armstrong performed the first successful docking of two vehicles in space.
But it was as spacecraft commander for Apollo 11 that he achieved worldwide fame, becoming the first man to land a craft on the moon and first to step on its surface.
Mr Armstrong and then wife Janet met Queen Elizabeth and Prince Andrew at Buckingham Palace at a reception following the moon-landing in 1969 during his 22-nation 38-day world tour.
Space agency Nasa tweeted tonight: "NASA offers its condolences on today's passing of Neil Armstrong, former test pilot, astronaut & the 1st man on the moon. Neil was 82."
Professor Colin Pillinger, the planetary scientist who was the driving force behind Britain's Mars lander Beagle 2, said Mr Armstrong "inspired an entire generation of scientists".
The scientist, who as a young man was involved in analysing samples brought back to earth by Apollo 11, told of meeting the astronaut.
"He said to me 'you analysed some of my samples'. I have dined out on that forever," he told BBC News.
"It is such a sad occasion."