With its American tough guy hero and a conveyor belt of terrorist attacks to foil, 24 accidentally became the zeitgeist marker for 2000s TV. The series—which was filmed before 9/11, but didn't air until after—starred Kiefer Sutherland as Counter Terrorist Unit (CTU) officer Jack Bauer and told an epic story of imminent threats and last-minute saves to the soundtrack of a beeping clock. It was an innovative show that presented events in as close to real-time as anything with commercials can get, filling an hour slot with an hour of in-universe action. For an espionage thriller, the structure was perfect for making the audience feel the claustrophobic constraints of having to work faster than your enemies.

Presidential assassination attempts, nuclear detonations, and cyberattacks were just a few of the potential catastrophes that Bauer tried his best to help prevent, regardless of the methods necessary. The ends always justified the means, which is why the show took on both the good and the evil elements of the post-9/11 culture in the United States, specifically in its positive portrayal of using torture to achieve counterterrorism goals.

An undeniable phenomenon, 24 resurrected Sutherland's career, earned massive audiences and prestige awards, and outlasted Mission: Impossible to become the longest-running American show about counterterrorism. Here are 25 surprising facts about the series, which premiered almost 20 years ago on November 6, 2001.

1. Originally, 24 was supposed to be about a wedding.

Joel Surnow's initial concept for 24 was solely about the real-time, ticking-clock format. So when Surnow called co-creator Bob Cochran to pitch the concept, the show was, at that point, about the day leading up to a wedding. That was quickly scrapped in favor of a thriller where someone's daughter was kidnapped, and eventually morphed into an anti-terrorist drama.

2. 24 borrowed several elements from La Femme Nikita.

La Femme Nikita, a TV series adapted by Surnow from the 1990 Luc Besson film of the same name, was a cult staple of 1990s action television. It was also a proving ground for what Surnow would do later with 24, including a hero killing in cold blood, terrorist attacks that don't get stopped, split screen formats, and even the name Bauer.

3. 24's producers almost scrapped the real-time format after season 1.

Fortunately, most of the actors—Sutherland included—lobbied the creators to keep it. Co-writer Virgil Williams told The Guardian that dropping the real-time format "would be like killing Tony Soprano."

4. The real-time format plagued 24's writers.

Carlos Bernard and Kiefer Sutherland in 24.20th Century Fox Home Entertainment

Despite saying that the format was freeing in certain aspects, writer Michael Loceff told Slate that it could also box them in and caused trouble for one simple reason: They couldn't magically transport people where they needed to be. "You want the character of Curtis to be at CTU, but he’s at the airport, so we can’t have him at CTU right then. And then the way we write the show adds to that, because although we do have a broad sense of the entire season’s arc, we write the episodes sequentially. So, you end up in situations where you need a character to be acting as if they’re at full capacity, but we just killed his mother or father. It seemed like a good idea at the time to kill their father or mother, but later it’s just damned inconvenient to have somebody mourning."

5. The clock on 24 went silent whenever a character died.

The show reminded viewers of its real-time gimmick with virtually every commercial break and credits sequence, ending scenes and episodes with its iconic digital clock beeping down the seconds. To mark the death of a major character or a moment of intense sadness, the clock would appear silently as a tribute. (They probably also did it because blaring a klaxon over and over might kill the impact of someone dying.)

6. Kiefer Sutherland got a tattoo to make filming on 24 easier.

Bauer has a tattoo of the Virgin of Guadalupe from his time in deep cover with the Salazar Brothers, but instead of spending hours in the make-up chair every time it appeared on screen, Sutherland got it for real. Presumably it was a big time saver—not to mention a lovely keepsake.

7. Jack Bauer limped in 24's second season because Kiefer Sutherland tripped coming out of his trailer.

In season 2, Jack Bauer survived a plane crash, but pulled a piece of wooden debris out of his leg and limped afterward. The crash was always part of the plan, but the massive splinter and limp became quick fixes for Sutherland's real-life limp, which occurred after he hurt himself stepping out of his trailer. They had to rewrite the show again when Carlos Bernard (who played Tony Almeida) dislocated his ankle during a basketball game, hobbling an epic fight scene between his and Jack's characters.

8. 24's infamous cougar bit Elisha Cuthbert.

Tough guy Sutherland may have hurt himself coming out of his trailer, but Elisha Cuthbert—who played Jack Bauer's daughter, Kim—was bitten by the show's infamous cougar from season 2. The cougar scene in "Day 2: 6:00pm - 7:00pm" is infamous for going over the top of the over-the-top treatment of her character, but she was hospitalized for it when the cougar bit her hand—and caused some unnecessary concern when she rolled into the ER covered in fake blood and fake injuries (for filming).

9. Sarah Clarke wore the same clothes for an entire season of 24.

Kiefer Sutherland and Sarah Clarke in '24'20th Century Fox Home Entertainment

Nina Myers is a massive part of 24, but Sarah Clarke was cast in the role at the very last minute—literally. The show was getting ready to kick off its first day of shooting when Clarke auditioned and was cast. Since she was shuttled straight from an audition to filming, the wardrobe department didn't have time to create a costume for her, so she ended up wearing the clothes she had auditioned in for a full season of filming.

10. A season 4 episode of 24 flashed a real cell phone number.

While most TV shows and movies use fake phone numbers (see: 555-5555), 24 used a valid cell phone number belonging to a crew member in "Day Four: 11:00am - 12:00pm," which became known as the Fan Phone. The voicemail message alerted callers that they'd called the 24 prop phone, but some fans got through to talk to writers, producers, production designers, and more. It also became a go-to number, so tons of characters all share the same phone number like it's some kind of party line.

11. There's a nod to Stand By Me in 24.

Kiefer Sutherland in Rob Reiner's Stand By Me (2006).Sony Pictures Home Entertainment

Milo Pressman is a character in Stand By Me who owns a junkyard (and a mean junkyard dog). Milo Pressman is also a character in 24. Either that's a major coincidence, or it's a subtle tip of the cap to the movie that helped launch young Sutherland's career.

12. Mary Lynn Rajskub was cast in 24 because of Punch-Drunk Love.

Mary Lynn Rajskub's Chloe O'Brian became one of the most important characters in the show after joining in its third season, but the fit wasn't always obvious. The actor got her start in stand-up comedy and cut her teeth on the absurdity of Mr. Show, but she was called into an audition because producer Peter Lenkov loved her as Adam Sandler's overbearing sister in Punch-Drunk Love and wanted to write a part for her.

13. It was Mary Lynn Rajskub's mom her convinced her to go to the 24 audition.

Mary Lynn Rajskub as Chloe O'Brian in 24.20th Century Fox Home Entertainment

Rarely having drama auditions, and still recovering from a really bad one, Rajskub was reluctant to read for 24. Though her agent pushed her to do it, she had another cheerleader in her corner: When her mom heard she had an opportunity to audition, she raved about 24. So Rajskub binged two seasons, liked it, and felt better about trying out. The world has Mrs. Rajskub to thank for Chloe's existence.

14. The show's producers announced 24's fourth season through a viral website used in an episode.

During Day 3, MI6-agent-turned-terrorist Stephen Saunders (Paul Blackthorne) uses SylviaImports.com as a mechanism for President Palmer to provide a list of covert sources around the world. Naturally, fans went straight for the site after its debut in the episode to find a special message: "A big thank from the crew of 24. Thanks for watching, we love making it for you, and yes, we did get picked up for Season 4."

15. Sean Astin joined the cast of 24 because of his chiropractor.

Sean Astin in 24.20th Century Fox Home Entertainment

Five years after the first The Lord of the Rings movie appeared in cinemas, Sean Astin joined the cast of 24 in its fifth season—and he landed the role in a rather unorthodox way. Astin just happened to see the same chiropractor as Surnow. One day, when both men were there for appointments, the chiropractor asked Astin if he wanted to meet Surnow; he said yes, and the two men proceeded to another room. Astin complimented the show, and Surnow—who was in his boxers—offered the actor a role right then and there.

16. The phone calls on 24 were filmed much differently than on other shows.

The vast majority of TV shows film an actor on a phone call with a script supervisor or other crew member reading the other character's lines, but the vast majority of TV shows don't see characters spending most of their time on the phone. For 24, that meant having both actors present for phone calls, which worked out well for actors like Leslie Hope (who played Jack's wife, Teri Bauer), who didn't share much screen time with Sutherland but felt close to him because she was right next to him for the phone calls.

17. The late John McCain was a 24 super-fan—and made a cameo in season 5.

Is there really anything that screams Bush-era anti-terrorism drama more than having a cameo from Senator John McCain? Yet instead of playing a Congressperson or Otherwise Important Person in a Suit, he can be seen for about a full second as a CTU staffer handing off a folder.

18. Several actors made repeat appearances on 24—but as different characters.

In an unusual move for a TV series (unless you're Law & Order), several actors returned to 24 as completely different people. Omid Abtahi played Safa in one episode of season 4 and had a recurring role as Jibraan Al-Zarian in season 7; Tony Todd played Detective Norris in season 3 and General Juman in season 7; and Anthony Aziz played Mamud Faheen in season 2 and Rafique in season 4.

19. David Palmer was the only president on 24 to serve his full term.

Dennis Haysbert as President David Palmer in 24.20th Century Fox Home Entertainment

24 went through 11 presidents in 18 years (of in-universe time). President Palmer (Dennis Haysbert) is the only one elected to office to actually finish a full term. One president was incapacitated during an attack on Air Force One; another was unseated when his involvement in terrorist activities was made public; one died by assassination; one resigned because of her involvement in an assassination cover-up; and one intimated that he left office early because of Alzheimer's. Others spent time as Acting President when another was temporarily removed with the 25th Amendment, and others stepped into the position midway through a full term.

20. Pretty much everyone in RoboCop was on 24.

That includes RoboCop himself, Peter Weller, as well as Ray Wise, Paul McCrane, Kurtwood Smith, Jesse D. Goins, and Edward Edwards.

21. Cherry Jones said she compromised her principles to appear on 24.

Cherry Jones in 24.20th Century Fox Home Entertainment

When asked by Terry Gross on NPR's Fresh Air how she felt about being a part of show that portrayed torture so regularly and positively, Jones said, "I compromised myself. And I did it because my parents were both in steep declining health."

Jones had been on Broadway when she got hired by 24 to play President Allison Taylor, and taking the job meant being able to be with her parents several weeks a month for the last years of their lives.

22. Jack Bauer killed a lot of people on 24.

And we mean a lot: Jack killed 270 people over eight seasons. That's 18 years in-universe, or 15 people a year—which makes our "hero" Jack much more prolific than your average serial killer.

23. Kim Bauer was abducted four times (including three times in season 1).

Elisha Cuthbert as Kim Bauer in 24.20th Century Fox Home Entertainment

Nicknamed "Spawn" by hateful fans, Jack's profoundly unlucky daughter was kidnapped three times in the first season alone, and experienced one more kidnapping in season 2 at the hands of a prepper who lied to her about an atomic bomb going off in Los Angeles. That doesn't count the handful of times she was detained by police or held up in a convenience store robbery. The only thing producers didn't do was tie her to train tracks.

24. There was almost a 24/Die Hard crossover.

We don't have a lot of details about how any of this went down, but in 2010, a deal was in the works for Sutherland to return as Jack Bauer alongside Bruce Willis's John McClane for a cross-over movie event. Tragically, it fell apart.

25. There are Indian and Japanese versions of 24.

Anil Kapoor guest stars in 24, which he later adapted for Hindi-speaking audiences20th Century Fox Home Entertainment

After appearing as President Omar Hassan of the fictional Republic of Kamistan, actor Anil Kapoor bought the rights to adapt 24 for a Hindi-speaking audience, and created two seasons of the series in which he starred as the Bauer-esque Jai Singh Rathod. Similarly, Toshiaki Karasawa starred in a Japanese version of the show where his CTU Japan Agent Genba Shidō must safeguard Urara Asakura (Yukie Nakama) as she prepares to be the first female prime minister.