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."
The end-of-decade goal was met with more than five months to spare. "Houston: Tranquility Base here," Armstrong radioed after the spacecraft settled onto the moon. "The Eagle has landed."
"Roger, Tranquility," Apollo astronaut Charles Duke radioed back from Mission Control. "We copy you on the ground. You've got a bunch of guys about to turn blue. We're breathing again. Thanks a lot."
The third astronaut on the mission, Michael Collins, circled the moon in the mother ship Columbia 60 miles overhead while Armstrong and Aldrin went to the moon's surface.
"He was the best, and I will miss him terribly," Collins said through NASA.
In all, 12 American astronauts walked on the moon before the last moon mission in 1972.
For Americans, reaching the moon provided uplift and respite from the Vietnam War, from strife in the Middle East, from the startling news just a few days earlier that a young woman had drowned in a car driven off a wooden bridge on Chappaquiddick Island by Sen. Edward Kennedy. The landing occurred as organizers were gearing up for Woodstock, the legendary three-day rock festival on a farm in the Catskills of New York.
Armstrong was born Aug. 5, 1930, on a farm near Wapakoneta in western Ohio. He took his first airplane ride at age 6 and developed a fascination with aviation that prompted him to build model airplanes and conduct experiments in a homemade wind tunnel.
As a boy, he worked at a pharmacy and took flying lessons. He was licensed to fly at 16, before he got his driver's license.