Armstrong became the first human to set foot on the moon on July 20, 1969. As he was about to step onto the dusty surface, he uttered the famous line: “That’s one small step for [a] man, one giant leap for mankind.”
The Twitter feed of NBC Nightly News said he died at 2:45 p.m. ET Saturday and that he had suffered complications from heart surgery he underwent earlier this month.
The ex-astronaut underwent cardiac bypass surgery just two days after his birthday on Aug. 5.
Edwin "Buzz" Aldrin, the colleague who also walked on the moon, sent out a statement late afternoon on Saturday.
"I know I am joined by millions of others in mourning the passing of a true American hero and the best pilot I ever knew," said Aldrin.
"My friend Neil took the small step but giant leap that changed the world and will forever be remembered as a landmark moment in human history. I had truly hoped that in 2019, we would be standing together along with our colleague Mike Collins to commemorate the 50th Anniversary of our moon landing. Regrettably, this is not to be. Neil will most certainly be there with us in spirit."
'The enormous power of one small step'
U.S. President Barack Obama hailed Armstrong as one of America's greatest heroes in a statement, calling Armstrong's first steps on the moon "a moment of human achievement that will never be forgotten."
"Neil’s spirit of discovery lives on in all the men and women who have devoted their lives to exploring the unknown – including those who are ensuring that we reach higher and go further in space. That legacy will endure – sparked by a man who taught us the enormous power of one small step."
NASA chief Charles Bolden recalled Armstrong's legacy: "[He] will be remembered for taking humankind's first small step on a world beyond our own."
CBC News Chief Correspondent Peter Mansbridge called the moon landing an unforgettable event — one that was watched by an estimated 600 million people.
"That was a day of a global village, to quote Marshall McLuhan, we were all sharing this one event."
Mansbridge, on the phone to CBC News Network, said he had the privilege of going to news conferences in the 1970s where Armstrong would be speaking.
"He didn’t seem very outgoing, he wasn't someone who couldn’t wait to get in front of a camera or microphone. He had a life that was without blemish," said Mansbridge.
"Neil Armstrong was a true hero."
Marc Garneau, who was the first Canadian to fly on a NASA mission to space, was 20 years old when Armstrong landed on the moon in 1969.
Garneau, who is now a Liberal MP, said he listened to Armstrong's lunar landing on the radio.
"It was a beautiful moon-lit night and I was seized by this historical moment and I didn’t really believe that it was possible. Of course, this was a great achievement, the first human being to set foot on another celestial body," Garneau said in an interview.
Garneau said Armstrong was a "modest" and "unassuming" man when he met him.
Born in Wapakoneta, Ohio, on Aug. 5, 1930, Armstrong went on to get a Bachelor of Science degree in Aeronautical Engineering from Purdue University and a Master of Science in Aerospace Engineering from the University of Southern California.
According to the NASA website, Armstrong joined the National Advisory Committee for Aeronautics (NACA) in 1955. NACA was the predecessor to the National Aeronautics and Space Administration (NASA). During his 17 years at NACA in Cleveland, he was an engineer, test pilot, astronaut and administrator.
Armstrong then became a research pilot at NASA's Flight Research Center in Edwards, Calif., and flew many pioneering high-speed aircraft. He flew over 200 different models of aircraft, rockets, helicopters and gliders, said the website.
Armstrong was upgraded to astronaut status in 1962. Assigned as command pilot for the Gemini 8 mission, he performed the first successful docking of two vehicles in space on March 16, 1966.
In reflecting on his historic moment on the moon, Armstrong said the "sights were simply magnificent, beyond any visual experience that I had ever been exposed to."
After the moon landing, Armstrong subsequently held the position of Deputy Associate Administrator for Aeronautics, NASA Headquarters, Washington, D.C.
Armstrong was known for his humility. Despite his fame, he never sought the spotlight. Appearing in Dayton, Ohio, in 2003 to celebrate the 100th anniversary of powered flight, Armstrong spoke for only a few seconds to a crowd of 10,000 before leaving the stage.
Former astronaut and senator John Glenn has described his friend and colleague as "exceptionally brilliant" but "rather retiring."
Eventually, he was a Professor of Aerospace Engineering at the University of Cincinnati between 1971 to 1979. And, from 1982 to1992, Armstrong was chair of Computing Technologies for Aviation, Inc., Charlottesville, Va.
His many honours include the Presidential Medal of Freedom, the Congressional Space Medal of Honour, the NASA Distinguished Service Medal and the Royal Geographic Society's Gold Medal.
Despite all the accolades, Armstrong said he always thought of himself as an engineer.
"I am, and ever will be, a white socks, pocket protector, nerdy engineer," he stated in one of his 2000 interviews. "And I take a substantial amount of pride in the acccomplishments of my profession."