The cause of Beckwith's death was not immediately released. He had malignant skin cancer, along with other health problems, he told Focus on the Family last year.
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Beckwith was already retired when terrorists hijacked two commercial planes and crashed them into the twin towers of the World Trade Center, killing 2,753 people. Another hijacked plane crashed that day into the Pentagon, killing 184 people, while 40 passengers and crew aboard a fourth hijacked plane died when their plane crashed in Shanksville, Pennsylvania.
Like many retired firefighters, Beckwith rushed to the scene of terror in Lower Manhattan - and he soon became a symbol of strength and resilience.
A grandfather's call to action
Beckwith, then 69, was enjoying life as a retired grandfather on Long Island when he heard the news on Sept. 11, 2001.
"I told my wife, 'I'm going down,'" Beckwith recalled in a 2005 interview with CNN.
His family tried to stop him from going to Ground Zero. But after Beckwith learned one of his colleague's sons was among the hundreds of firefighters missing, he put on his old uniform, strapped on his helmet and rushed out the door.
"I go start digging with the guys in the North Tower, and we come across a pumper with a 76 Engine," Beckwith said. "And we're working because we're looking for survivors and we're looking for people, and we're hoping they found an air pocket or something."
During that devastating first week of horror, heartbreak and hope, word trickled down among rescuers that Bush was going to visit Ground Zero. Beckwith climbed atop the charred hull of a fire engine to try to get a better look at where he thought the then-president might speak.
Beckwith was alone atop the truck when a man he assumed was Secret Service approached him. It turned out to be Bush's deputy chief of staff, Karl Rove.
"He comes over and he dusts off (the spot) next to my foot and he says, 'Is this safe?'" Beckwith recalled.
RELATED: 9/11/01 timeline: How the September 11, 2001 attacks unfolded
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Rove then told Beckwith "someone important" would come over and asked the retired firefighter to help give the VIP a hand up onto the truck and then leave his location. Beckwith agreed.
"And the president came, and he is shaking hands with all the ironworkers and all the cops and all the firemen that were down there ... and I figure he's going over to the microphones, but he makes a quick right, and he puts his arm up and I said, 'Oh my God!'"
After helping Bush onto the truck, Beckwith started to crawl down - but the president stopped him.
"He says, 'Where are you going?' I said, 'Uh, I was told to get down.' He said, 'No, no, you stay right here.'"
As chants of "U-S-A, U-S-A" settled down, Bush started speaking. Still, someone from the crowd yelled they could not hear him.
Bush draped his arm around Beckwith, then said, "I can hear you. The rest of the world hears you. And the people who knocked these buildings down will hear all of us soon." The crowd erupted in cheers.
Images of Beckwith - stoic but resolute - with the president's hand on his shoulder became an iconic symbol of fortitude.
A lasting legacy
Beckwith also made an impression on the president himself.
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"Do you remember the Time magazine where the president is holding up the flag? He wanted me to have that flag," Beckwith told CNN in 2005. "I still have it."
Bush later reflected on his decision to address the crowd at Ground Zero alongside Beckwith.
"I felt like I needed to say something. And I got up on a pile of rubble, and I wanted a firefighter to be with me," Bush said. "It was a statement of solidarity and, so I get up on this fire - it turns out to be a fire truck that had been destroyed."
"It was a very emotional moment," Bush continued. "The whole event was emotional because I was looking in the eyes of people who had rushed into danger to find loved ones and coworkers and people that they cared about."
In his later years, Beckwith visited Bush in the Oval Office and was immortalized in wax at the Presidential Wax Museum near Mount Rushmore in South Dakota.
And even in retirement, Beckwith was a steadfast activist for firefighters, traveling internationally, speaking and raising money for the New York Firefighters Burn Center Foundation.
"A fireman is a fireman," he said in 2005. "You're in a family of great people."
CNN's Josh Campbell and Zenebou Sylla contributed to this report.