On the morning of Sept. 11, 2001, 34-year-old New York City firefighter Stephen Siller had just finished his overnight shift when he heard a call come in on the scanner.

"He immediately knew something was awry," so he drove to his firehouse in Brooklyn, his son, Stephen Siller Jr., told ABC News.

"When he got there, he realized his whole unit had responded [to the World Trade Center]," Siller Jr. said. "So he grabbed his gear, threw it in his truck and started to make his way to the World Trade Center. But on 9/11, they shut down every entryway into Manhattan."

He parked his car by the Brooklyn Battery Tunnel, Siller Jr. said, put about 60 pounds of gear on his back, and ran through the tunnel to the South Tower of the World Trade Center.

Stephen Siller was among 343 New York City Fire Department members killed on 9/11. He was survived by his close-knit siblings, his wife Sally, and his five children, including Stephen Jr., who was 9 months old.

Siller Jr., now 25, doesn't have his own memories of his father, but he's poured his energy into honoring those who died on 9/11.

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When American Airlines Flight 77 slammed into the Pentagon, FBI Special Agent Jeffrey Miller rushed to the scene, spending weeks on site recovering evidence from the burned wreckage.

Now, two and a half decades later, he is one of the many FBI agents that are suffering from the long-lasting effects of that day.

So far more than 30 FBI personnel have died from cancer or other illnesses the FBI says are related to exposure to toxic material at the 9/11 sites. Miller says he personally knows at least a dozen of them.

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Chef Don Pintabona spent years cooking up the finest dishes for celebrities, Wall Street brokers and other VIPs at the Tribeca Grill in downtown Manhattan, but nothing could have prepared him and the rest of the city's restaurant community for their biggest job.

In the hours after the World Trade Center was attacked and destroyed on Sept. 11, 2001, Pintabona said he and many other chefs, caters, food service workers and others all yearned to help the city in some capacity with their skills, but didn't immediately know how.

But through quick thinking, organizing and the generosity of thousands of New Yorkers, Pintabona and the other restaurant members put together a massive operation that fed Ground Zero workers around the clock for two months after the attacks.

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Jack Moran Jr. spoke with ABC News Live about the legacy of his friend Welles Crowther, a 9/11 hero who has been dubbed the "man in the red bandana.”

“He saved the lives of 18 people -- he’s a hero,” Moran said. “And it’s very important to know his story.”