His first words after the feat are etched in history books and the memories of the spellbound millions who heard them in a live broadcast.
"That's one small step for man, one giant leap for mankind," Armstrong said. He insisted later that he had said "a'' before man, but said he, too, couldn't hear it in the version that went to the world.
Armstrong, who had bypass surgery earlier this month, died Saturday at age 82 from what his family said were complications of heart procedures. His family didn't say where he died; he had lived in suburban Cincinnati.
He was "a reluctant American hero who always believed he was just doing his job," his family said in a statement.
The moonwalk marked America's victory in the Cold War space race that began Oct. 4, 1957, with the launch of the Soviet Union's Sputnik 1, a 184-pound satellite that sent shock waves around the world. The accomplishment fulfilled a commitment President John F. Kennedy made for the nation to put a man on the moon before the end of 1960s.
Armstrong and Buzz Aldrin spent nearly three hours walking on the lunar surface, collecting samples, conducting experiments and taking photographs.
"The sights were simply magnificent, beyond any visual experience that I had ever been exposed to," Armstrong once said.
In those first few moments on the moon, Armstrong stopped in what he called "a tender moment" and left a patch to commemorate NASA astronauts and Soviet cosmonauts who had died in action.
Although he had been a Navy fighter pilot, a test pilot for NASA's forerunner and an astronaut, the modest Armstrong never allowed himself to be caught up in the celebrity and glamour of the space program.
"I am, and ever will be, a white socks, pocket protector, nerdy engineer," he said in 2000 in one of his rare public appearances. "And I take a substantial amount of pride in the accomplishments of my profession."
Rice University historian Douglas Brinkley, who interviewed Armstrong for NASA's oral history project, said Armstrong fit every requirement the space agency needed for the first man to walk on moon, especially because of his engineering skills and the way he handled celebrity by shunning it.
"I think his genius was in his reclusiveness," said Brinkley. "He was the ultimate hero in an era of corruptible men."
Fellow Ohioan and astronaut John Glenn, one of Armstrong's closest friends, recalled Saturday how Armstrong was on low fuel when he finally brought the lunar module Eagle down on the Sea of Tranquility.
"That showed a dedication to what he was doing that was admirable," Glenn said.
A man who kept away from cameras, Armstrong went public in 2010 with his concerns about President Barack Obama's space policy that shifted attention away from a return to the moon and emphasized private companies developing spaceships. He testified before Congress, and in an email to The Associated Press, Armstrong said he had "substantial reservations."
Along with more than two dozen Apollo-era veterans, he signed a letter calling the plan a "misguided proposal that forces NASA out of human space operations for the foreseeable future."
Armstrong was among the greatest of American heroes, Obama said in a statement.
"When he and his fellow crew members lifted off aboard Apollo 11 in 1969, they carried with them the aspirations of an entire nation. They set out to show the world that the American spirit can see beyond what seems unimaginable — that with enough drive and ingenuity, anything is possible," Obama said.
Obama's Republican opponent Mitt Romney echoed those sentiments, calling Armstrong an American hero whose passion for space, science and discovery will inspire him for the rest of his life.
"With courage unmeasured and unbounded love for his country, he walked where man had never walked before. The moon will miss its first son of earth," Romney said.
NASA Administrator Charles Bolden recalled Armstrong's grace and humility.
"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," Bolden said in a statement.
Armstrong's modesty and self-effacing manner never faded.
When he appeared in Dayton in 2003 to help celebrate the 100th anniversary of powered flight, he bounded onto a stage before a packed baseball stadium. But he spoke for only a few seconds, did not mention the moon, and quickly ducked out of the spotlight.
He later joined Glenn, by then a senator, to lay wreaths on the graves of Wilbur and Orville Wright. Glenn introduced Armstrong and noted that day was the 34th anniversary of his moonwalk.
"Thank you, John. Thirty-four years?" Armstrong quipped, as if he hadn't given it a thought.
At another joint appearance, Glenn commented: "To this day, he's the one person on earth I'm truly, truly envious of."
Armstrong's moonwalk capped a series of accomplishments that included piloting the X-15 rocket plane and making the first space docking during the Gemini 8 mission, which included a successful emergency splashdown.
In the years afterward, Armstrong retreated to the quiet of the classroom and his southwestern Ohio farm. In an Australian interview earlier this year, Armstrong acknowledged that "now and then I miss the excitement about being in the cockpit of an airplane and doing new things."
Glenn, who went through jungle training in Panama with Armstrong as part of the astronaut program, described him as "exceptionally brilliant" with technical matters but "rather retiring, doesn't like to be thrust into the limelight much."
The 1969 landing met an audacious deadline that President Kennedy had set in May 1961, shortly after Alan Shepard became the first American in space with a 15-minute suborbital flight. (Soviet cosmonaut Yuri A. Gagarin had orbited the Earth and beaten the U.S. into space the previous month.)
"I believe this nation should commit itself to achieving the goal, before the decade is out, of landing a man on the moon and returning him safely to Earth," Kennedy had said. "No single space project in this period will be more impressive to mankind, or more important to the long-range exploration of space; and none will be so difficult or expensive to accomplish."