President Barack Obama and astronaut Buzz Aldrin led tributes Saturday to the famed Apollo 11 commander Neil Armstrong, the first man on the moon, lauding him as a reluctant but true American hero.

Armstrong, who died from complications following cardiac bypass surgery, was praised for his willingness to embrace and then conquer challenges that had once seemed impossible.

"When he and his fellow crew members lifted off aboard Apollo 11 in 1969, they carried with them the aspirations of an entire nation," said Obama, who was two weeks short of his eighth birthday when the historic mission succeeded.

"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," he added in a statement.

"When Neil stepped foot on the surface of the moon for the first time, he delivered a moment of human achievement that will never be forgotten."

Aldrin, who with Armstrong was watched by an estimated global television audience of 500 million as they gingerly bounced on the moon's surface in their chunky spacesuits, praised his comrade's skill, dedication and selflessness.

"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," Aldrin said, noting that his thoughts were with Armstrong's devastated but proud family.

"I will miss my friend Neil as I know our fellow citizens and people around the world will miss this foremost aviation and space pioneer."

The third Apollo 11 astronaut -- Michael Collins, the command module pilot who orbited the moon while his crewmates landed -- said Armstrong "was the best, and I will miss him terribly."

Armstrong, a Korean War veteran who was decorated by 17 countries and received a slew of US honors, was never comfortable with the worldwide fame that stemmed from the Apollo 11 mission, and he shied away from the limelight.

"He didn't feel that he should be out huckstering himself," John Glenn, the first American to orbit Earth told CNN, recalling Armstrong's legendary humility.

"He was a humble person, and that's the way he remained after his lunar flight, as well as before," the former Ohio senator added.

For the United States, the Apollo 11 mission was a Cold War maneuver, a bid to fulfill the vow made by President John F. Kennedy that NASA could overtake the pioneering Russian space program and put a man on the moon.

And for spellbound audiences around the world, it was also an extraordinary and optimistic voyage of discovery and engineering, whose achievements had a profound effect on space and aviation, said Obama.

"Neil was among the greatest of American heroes -- not just of his time, but of all time," the president said. "Neil's spirit of discovery lives on in all the men and women who have devoted their lives to exploring the unknown."

Obama's Republican challenger for the White House, Mitt Romney, said the space pioneer was an inspiration who now "takes his place in the hall of heroes."

"With courage unmeasured and unbounded love for his country, he walked where man had never walked before," said Romney, who spoke with Armstrong just a few weeks ago. "The moon will miss its first son of Earth."

Republican House Speaker John Boehner said: "A true hero has returned to the heavens to which he once flew."

And US Secretary of Defense Leon Panetta bid farewell on behalf of the American military to one of its own.

"As a decorated Korean War veteran, as an astronaut for NASA, and as the first man to walk on the moon, Neil inspired generations of Americans to believe that as a nation we are capable of achieving greatness that only comes with determination, perseverance and hard work," said the Pentagon chief.

Australian Prime Minister Julia Gillard said Armstrong's death "marks the end of an amazing era in human progress."

"His example of service, accomplishment and modesty... will never die," she added.