Welles Crowther, a 24-year-old former volunteer firefighter, worked a finance job in the South Tower when terrorists struck on Sept. 11, 2001.

After his heroism that day, he became known to many as, simply, "the man in the red bandana," who gave his life so that others might live.

At the dedication of the 9/11 Memorial and Museum in New York today, President Obama paid tribute to the men and women who lost their lives when terrorists struck nearly 13 years ago. Their final moments, he said, were a testament to the "true spirit of 9/11: love, compassion, sacrifice."

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In particular, Obama singled out Crowther's story.

"In those awful moments after the South Tower was hit, some of the injured huddled in the wreckage of the 78th floor. The fires were spreading; the air was filled with smoke. It was dark, and they could barely see. It seemed as if there was no way out," Obama said.

"And then, there came a voice: clear, calm, saying he had found the stairs. A young man, in his 20s, strong, emerged from the smoke and, over his nose and his mouth, he wore a red handkerchief. … He led those survivors down the stairs to safety and carried a woman on his shoulders down 17 flights," the president said. "And then he went back."

Since then, "a generation of service members, our 9/11 generation, have served with honor … [and] our SEALs made sure justice was done," Obama added, referring to the assault on the Pakistan compound of 9/11 mastermind Osama bin Laden.

But, the president said, ours is "a nation that stands tall and united and unafraid because no act of terror can match the strength and character of our country. Like the great wall and bedrock that embrace us today, nothing can ever break us."

Obama, who earlier joined first lady Michelle Obama, former President Bill Clinton, and former Secretary of State Hillary Clinton on a tour of the newly opened facility, reminded guests that "we tell their story so that generations yet unborn will never forget … men and women who rushed into an inferno."

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He then introduced Crowther's mother, Alison Crowther.

As her husband mouthed the words of her speech from his seat in the audience, Alison Crowther echoed the president's message:

"We could not be more proud of our son," Crowther said. "It is our greatest hope that when people come here and see Welles' red bandana, they will remember who people helped each other that day. And we hope that they will be inspired to do the same, in ways both big and small. This is the true legacy of Sept. 11."

Ling Young, one of the women Welles saved, accompanied Crowther onstage, saying simply, "I'm here today because of Welles, a man I did not get the chance to thank. It was hard for me to come here today, but I wanted to do so, so I could thank his parents, my new friends, Jeff and Alison."

ABC News' Mary Bruce contributed to this report.