(NewsNation) — 21 years ago, 19 terrorists hijacked four commercial planes. The hijackers intentionally ran two of them into the Twin Towers at the World Trade Center, flew a third into the Pentagon and crashed the fourth into a field in Pennsylvania after people on the plane developed a counterattack against them.

Nearly 3,000 people were killed on September 11, 2001. The single largest loss of life resulting from a foreign attack on American soil happened at the hands of al-Qaeda. While we will never forget what happened, this is not their story. This story is about a true American hero, a man who put his life on the line to save nearly 2,700 others, cutting the death toll in almost half.

Rick Rescorla worked as the head of security for Morgan Stanley in the South Tower. The 62-year-old Vietnam veteran fought for enhanced safety measures at his place of work, especially after the 1993 terrorist bombing in the North Tower’s basement that left six people dead.

Ever since, Rescorla always worried there would be another attack and suspected the World Trade Center to be a target. It’s why he insisted Morgan Stanley workers perform escape drills on a regular basis. At the direction of Rescorla, Bill McMahon was one of the employees who practiced moving quickly down from 22 floors in the South Tower.

“He was convinced that this was going to happen again. He just didn’t know how, but he knew something was going to happen,” employee Bill McMahon said. “Rick was just this kind of laser-like focus on making sure everybody knew what to do if something happened, which was simply go to the fire escape stairwells, get out of the building, period. That’s it. Just get out of it. Don’t go up, go down, get out of the building.”

Rescorla had warned his wife Susan of a feeling that he had that something was going to happen – as if he could just sense it. Months before the attacks, he would tell her he had premonition-like feelings another attack was going to happen.

“He was trying to tell me that he thought something would happen,” Susan said. “And he wanted to tell me what he wanted me to do.”

Fast forward to September 11, 2001, disaster struck. Both towers of the World Trade Center hit, thousands running for their lives, in what we know now was a terrorist attack.

McMahon was in his Morgan Stanley office on the 44^th floor of the South Tower when he realized a plane hit their building.

“It blew out all the elevator banks. All the doors blew off and knocked us all over. The building kind of tips and comes back. It doesn’t seem that much when you watch it on TV, but when you were in the building, it literally moved back and forth,” McMahon said. “It moved back and forth, and it finally stopped. Then everybody realized at that point in time that it’s time to get out.”

McMahon and his colleagues knew exactly what to do thanks to Rescorla. 

“He taught us that, you know, there’s just three things you need to know, which is get to the elevator, don’t get to the stairwell, go down the stairwell, not up the stairwell and get away from the building. It’s just that simple, right? And so no matter what crazy things are going on, no matter what the port authorities telling you, okay, no matter what you’re hearing from anybody else, or hearing on the news, or whatever it may be, get to the stairwell, go down the stairwell, get out of the building,” McMahon said.

Amid the chaos, Rescorla picked up his megaphone as he had done many times before. And despite receiving official instruction to stay in place, he refused and told the workers to follow his evacuation plan. He led nearly 2,700 workers out of the office. As they filed down the stairs, McMahon says Rescorla sang songs, keeping everyone calm.

“He’s telling everybody be cool, everyone’s going to be good. You know, that’s kind of what he did, right? To calm everybody down. He did a phenomenal job with it and kept doing that,” McMahon said. “Then, we get out of the building. We were about, I’m going to say, four or five blocks away when the building collapsed.”

Once it seemed like they were all evacuated, Rescorla decided to go back in and make sure no one was left behind.

“Rick said, ‘You know what, I gotta go up now and sweep the floors and make sure that everybody’s out of the building,’” McMahon said.

Rick went back up with firemen because he wanted to make sure that everyone on the top floor was out. It was the last time anyone reportedly saw Rescorla alive.

He was at the top of building, still efforting the evacuation, when United Airlines Flight 175 hit the South Tower, prompting it to collapse.

Rescorla’s wife remembers their final conversation.

“Right before the towers came down, he called me and he said to me, ‘If something happens to me, I just want you to know that you made my life,’” Susan recounted.

Susan received a call from Rick’s best friend telling her to turn on the television.

“And that’s when I saw everything come down,” she said.

Susan said she thought she was prepared, but when the towers came down, the loss was unbearable.

Rick didn’t make it out of the building, but because of him, nearly 2,700 people did.

Still, McMahon said knowing Rick, if him making it out of the towers meant someone else didn’t, he wouldn’t have had it any other way.

“Rick is just a true American hero,”  McMahon said. “Rick saved the lives of 2,500 people … He touched people’s lives. I think the only thing I’d say about Rick is that was a calling for him. He wanted to make a difference in people’s lives, and he did.”

It’s something Susan hopes to continue in his memory. Since the attack, Susan has been traveling, gaining perspectives from all over the world on what people thought about the Sept. 11 terrorist attack. She wants to make sure no one forgets about what happened in America that September morning. She explained it’s her way of coping with the pain.

Susan said she will never forget, and that she will love Rick for the rest of her life.