Story highlights Lisa Jefferson was the Airfone operator who prayed with United passenger Todd Beamer

Josephine Harris survived the collapse of the World Trade Center's North Tower

Rudy Giuliani earned the moniker "America's mayor" in the days after the 9/11 attacks

Khalid Sheikh Mohammed, the 9/11 mastermind, is being held at Guantanamo Bay, Cuba

A voice on the phone. A cry in the dark. A flag raised amid death and devastation.

These are the stories forever linked with the September 11, 2001 , terror attacks in New York, Washington and western Pennsylvania.

In some cases, they are tales of ordinary people caught in extraordinary circumstances -- people who became symbols of comfort and hope for a grieving nation.

Then there were those who were behind the attacks, people who have become the emblem of evil.

On the 13th anniversary of the attacks, here is a look at some of those people -- then and now:

Lisa Jefferson, the voice

Then:

Hers was the voice on the other end of the line for Todd Beamer, the passenger aboard United Flight 93 whose last purported words -- "let's roll" -- became a rallying cry for the nation in the days following the terror attacks.

It was 9:45 a.m., when Beamer placed a call to an operator at a Verizon Airfone call center in Chicago and relayed that the airplane bound for San Francisco had been hijacked. The operator turned the call over to Jefferson, the supervisor on duty.

Photos: Photos: Remembering 9/11 Photos: Photos: Remembering 9/11 Remembering 9/11 – A group from the U.S. Navy gathers Thursday, September 11, at the Flight 93 National Memorial in Shanksville, Pennsylvania. This year marks the 13th anniversary of the September 11 terrorist attacks that killed nearly 3,000 people in New York, Washington and western Pennsylvania. Hide Caption 1 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – A woman bows her head in prayer in Shanksville, where United Airlines Flight 93 went down. Hide Caption 2 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – Family members gather in the rain at the impact site in Shanksville. Hide Caption 3 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – From left, U.S. President Barack Obama, U.S. Defense Secretary Chuck Hagel and Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey stand on stage as they participate in a ceremony at the Pentagon. Hide Caption 4 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – Obama and Hagel bow their heads during the ceremony at the Pentagon. Hide Caption 5 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – A woman reaches out to touch a rose on one of the benches at the Pentagon Memorial. Hide Caption 6 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – Tyrone McClave, of Bristol, Pennsylvania, looks up at One World Trade Center during a moment of silence in New York. Hide Caption 7 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – Members of the New York Police Department, the New York Fire Department and the Port Authority Police Department carry an American flag past one of the reflecting pools during memorial observances at the World Trade Center site. Hide Caption 8 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – Members of the New York Fire Department take time to reflect. Hide Caption 9 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – Paola Braut, of Belgium, kisses a photograph of her son Patrice along the edge of the North Pool of the World Trade Center site. Hide Caption 10 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – A man stands across the street from the National September 11 Memorial & Museum in New York. Hide Caption 11 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – Eileen Esquilin hugs her husband, Joe Irizarry, while mourning the loss of her brother, Ruben Esquilin Jr., during memorial observances in New York. Hide Caption 12 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – Former New York Gov. George Pataki, left, and former New York City Mayor Rudy Guiliani were among those in attendance at the World Trade Center. Hide Caption 13 of 14 Photos: Photos: Remembering 9/11 Remembering 9/11 – Sam Pulia, the mayor of Westchester, Illinois, and a former police officer of the same town, mourns over the name of his cousin, New York firefighter Thomas Anthony Casoria, who was killed on 9/11. Hide Caption 14 of 14

Beamer was calm as he detailed how three men had taken over the flight. Two had knives and had locked themselves in the cockpit, and one had a bomb strapped to his waist.

He told Jefferson about his children and his wife, Lisa.

"I had asked him, did he want me to place his call through to his wife for him. He told me that he didn't want me to put him through to her in case he didn't have to. He had hoped on landing that plane safely. And he told me if I didn't make it, would I please call her and let her know how much he loved her and his family," she told CNN in 2002.

"... After we said 'The Lord's Prayer,' the plane took another dive. And Todd said they had a plan. The next thing he said, 'Are you ready? OK, let's roll,'" she told CNN in 2001.

"And that's the last I heard from him.''

In the days that followed, she relayed Beamer's message to his wife.

Now:

Jefferson, 57, no longer answers telephone calls at the call center. She's changed jobs.

Most of her colleagues now don't know that she was the calm, caring voice who prayed with Beamer in his final minutes.

Sure, she's talked about it in the years since. At the urging of others, she even told her story in the book "Called: Hello, My Name is Mrs. Jefferson, I Understand Your Plane is Being Hijacked?"

The story of that conversation has been told and retold -- in books and articles, in movies and television shows.

But during a recent interview, Jefferson asked that no details about her current job or employer be made public.

"Every time I tell the story, it's like the first time," she said. "... I'm not a hero. I was just doing my job."

That day, after she took over the call, she said she turned around to hand off the phone to someone else. But, she says, there was no one there.

"I had to stay on the line," she said. "I stayed with him until the end."

She has credited her faith with giving her the strength to offer comfort and care during that 15-minute call.

"God had a purpose for me with the Beamer family," she said.

Josephine Harris, the angel

JUST WATCHED Rescuing Josephine Harris Replay More Videos ... MUST WATCH Rescuing Josephine Harris 01:46

Then:

Her story of survival is wrapped up with six firefighters who say they made it through the collapse of the World Trade Center's North Tower because they were trying to rescue her.

Harris, like so many, was trying to make her way down the stairwell of the North Tower.

Flight after flight, she descended. She stopped on the 20th floor, physically unable to take another step on her own.

The firefighters of Ladder Company 6 were on the 27th floor or so of the building and still climbing when then-Capt. Jay Jonas got a call on the radio that the South Tower had collapsed and he needed to get his men out of the North Tower.

"It was an almost empty feeling that we couldn't help anyone," Jonas, now a deputy chief, said this week.

As they were making their way down the stairwell, they found Harris. There she was, crying in the doorway, Jonas said.

"Hey Cap, what do you want us to do?" one of the firefighters asked. "Take her with us," Jonas said.

Half-carrying Harris, the firefighters continued to make their way down, slowly.

The clock was ticking.

By the time they made it to the fourth floor, Harris fell to the ground.

Leave me, she ordered the firefighters. They, of course, refused.

Then it happened. The 110-story building collapsed.

"It seemed like forever," Jonas said. It was only 13 seconds.

When it was over, Harris and the men of Ladder 6 were alive, entombed in the debris.

"There was only one time she lost her composure," Jonas said. "She said she was afraid, and she started to cry."

Without orders from the captain, the firefighters took turns caring for Harris until hours later when the thick dust settled and they were able to see a way to get out and get help.

"She was definitely alive because of us," Jonas said.

And they were alive because of her.

"She chose the fourth floor to stop, to fall to the floor," he said. "... Nobody survived above the fifth floor or on the first floor. If we hadn't stopped there, who knows? We probably wouldn't have survived."

Now:

In the years that followed, Harris became known at the "Angel of Ladder Company 6," and she and the firefighters stayed in contact.

Their story resonated with many people post-September 11, and they made appearances together at parades and dedications.

"If Josephine got a call to do an interview or an appearance, she would always call and make sure we were OK with it," Jonas said. "We would always tell her yes, and we'll be there with you."

On Jan. 12, 2011, Harris called 911 from her Brooklyn apartment.

By the time firefighters arrived, she had died of an apparent heart attack.

Jonas got the news in a telephone call from a firefighter. "It was like losing a member of your family, and she really was a member of the (Ladder 6) family," he said.

What neither he nor the other firefighters knew was that Harris was destitute. "She was an intensely private person," Jonas said.

For days, her body lay uncollected at the city morgue. Her family didn't have enough money to bury her.

"I thought 'Man, she's going to Potter's Field, if we don't do something," Jonas said.

So he got on the phone to the other firefighters, and they started to spread the word across the city.

They were soon contacted by the owner of Greenwich Village Funeral Home, who had heard of Harris' death. He remembered the story of the "guardian angel" of Ladder 6 and offered to pick up the entire cost of the service.

Jonas and the firefighters carried Harris one last time. They served as pallbearers, carrying her casket engraved with the words "guardian angel.''

George Johnson, Daniel McWilliams and William Eisengrein, the firefighters

JUST WATCHED Where is iconic 9/11 flag? Replay More Videos ... MUST WATCH Where is iconic 9/11 flag? 02:07

Then:

It was late afternoon, hours after the attacks, and the three firefighters joined the rush to what would become known as ground zero.

Eisengrein was sitting on his truck when he saw McWilliams carrying an American flag, he told ABCNews.com in 2011. Walking alongside McWilliams was another firefighter, Johnson.

Eisengrein knew McWilliams but had never met Johnson.

It is believed McWilliams found the flag from a yacht, "Star of America," docked nearby on the Hudson River, according to the CNN documentary "The Flag."

Eisengrein told ABC News he just knew McWilliams was going to hang it somewhere, and shouted out to him: "Do you need help?"

The three men found a flagpole leaning against a construction trailer, he said.

"So we put a piece of tin on the ground up to the trailer and hiked up that, and raised it," Eisengrein said.

"... We stood there and looked at it for a second and went about our ways."

None of them knew that their picture had been taken by Tom Franklin, a photographer with The Record in Bergen County, New Jersey.

Soon the picture was picked up by The Associated Press and splashed across newspaper front pages, becoming one of the iconic images associated with September 11.

Now:

Much has been made about the flag, and its whereabouts

Within hours of its raising, the flag disappeared from the World Trade Center site.

The makers of "The Flag" spoke with several photographers about going to ground zero and the heartbreaking scenes that awaited.

Among those interviewed was the couple who owned the yacht from which the flag was taken.

The couple wanted to donate the flag to the Smithsonian Institution and asked about a year after the attacks to borrow the signed flag briefly for a ceremony.

"When we got the flag, we were quite stunned that it was the wrong flag," said Shirley Dreifus. "... This wraps around the two of us, and we're not the thinnest people on Earth ... So we knew right away it was the wrong flag."

While the search for the flag continues, Johnson, McWilliams and Eisengrein rarely talk publicly about that day and the flag. They have routinely declined media requests for interviews over the years.

The firefighters "in question have repeatedly expressed no interest in interviews or additional media coverage," the FDNY said in an email response to a CNN request this week.

Maybe we know all we need to know about the three men: They did their job, and they reminded everyone by raising the flag that the country was still standing.

Rudy Giuliani, the mayor

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Then:

Giuliani was in the final days of his second term as mayor when an airplane crashed into the World Trade Center's North Tower. Giuliani was at the World Trade Center, getting an update on the rescue effort, when a second plane struck the South Tower.

The mayor, like many that day, was forced to run for his life when the tower came down.

He was engulfed in a cloud of debris, but famously kept his composure.

"This is a vicious, unprovoked act, a horrible attack on innocent men, women and children. It's one of the most heinous acts, certainly, in world history," he told CNN that day.

As New York mourned the loss of thousands of lives and cleaned up the debris, Giuliani seemed to be everywhere -- holding news conferences, giving interviews and attending funerals and fundraisers.

In the aftermath of the attacks, he earned the moniker "America's mayor" for the comfort he offered not only to city of more than 8 million, but to a shell-shocked nation.

Now:

Giuliani's popularity soared, spurring him to make a bid for the Republican presidential nomination in 2008.

But his campaign stumbled, badly.

Giuliani skipped the early primary states, staking his bid on a win in Florida. He finished third and pulled out of the campaign.

He quickly reinvented himself as a political pundit, becoming a regular on television news programs.

These days, the former mayor balances running Giuliani Partners, a security consulting firm, and working as a managing partner in the Bracewell & Giuliani law firm.

He even did a stint as a pitchman for LifeLock, the identify theft protection company. The company was a client of Giuliani Partners, he has said.

Even now, more than a decade later, the events of September 11 are never far from his thoughts.

"I think the most difficult moment I had as mayor of New York City was when I arrived at the World Trade Center," Giuliani said during a 2013 interview on "Oprah: Where Are They Now."

"Not really knowing how bad it was, not really emotionally grasping all of that until I saw a man throw himself out of the 100th floor. And that's an image -- that's an image that stayed with me forever, almost every day it comes up in my mind somehow. And then, after that, I just decided well, it's part of me and I have to live with it."

Khalid Sheikh Mohammed, the man who planned the attacks

Khalid Sheikh Mohammed.

Then:

Considered one of Osama bin Laden's most-trusted associates, the American-educated Mohammed was a wanted man long before the September 11 attacks.

He had already built up a reputation for plotting attacks against the United States and its allies abroad. In 1996, he was indicted for his alleged role in the 1995 plot to blow up 12 airliners bound from the Philippines for the United States.

Intelligence officials would later say that Mohammed had a fascination with airplanes, and that it was his idea to use the aircraft as weapons.

Mohammed is believed to have hatched the September 11 attacks in 1999, talking bin Laden into the plan, intelligence officials said.

In October 2001, Mohammed was among the initial 22 people named to the FBI's Most Wanted Terrorists list.

By 2002, authorities from a number of countries were on Mohammed's trail for his alleged role in the attempt by Richard Reid to use a shoe bomb to blow up an airliner, a bombing at a Bali nightclub and an attack on a synagogue in Tunisia.

He was finally captured March 1, 2003, in Rawalpindi, Pakistan, after an informant gave him up, according to accounts.

Now:

In a 26-page transcript of a tribunal hearing released by the Pentagon in 2007, Mohammed admitted to decapitating Wall Street Journal reporter Daniel Pearl and planning the September 11 attacks.

"I was responsible for the 9/11 operation, from A to Z," he said, according to the transcript.

He also took responsibility for the shoe bomb attempt, the nightclub bombing, the 1993 World Trade Center attack and a number of other attempted attacks that did not play out, according to the account offered by the transcript.

The United States has said it is seeking the death penalty against Mohammed for the September 11 attacks that left nearly 3,000 people dead.

He has been charged with conspiracy, murder in violation of the law of war, attacking civilians, attacking civilian objects, intentionally causing serious bodily injury, destruction of property in violation of the law of war, hijacking aircraft and terrorism.