On September 20, 1999, the first Law & Order spinoff series premiered. Law & Order: Special Victims Unit -- commonly known simply as SVU -- gives viewers a look at the detectives who investigate sex crimes that are, according to the opening narration, "considered especially heinous." Its two charismatic stars, Christopher Meloni and Mariska Hargitay, were a quick hit with audiences, and eventually the show's ratings surpassed that of the original Law & Order.

The show has seen multiple cast members come and go, in addition to legions of recurring characters and big changes in the lives of its regular players. Hargitay's Olivia Benson has become the commanding officer of the unit and the show is now the longest-running scripted non-animated series still on the air.

To celebrate all of its sordid stories, moments of heroism, fascinating characters, mind-blowing guest stars, and endless twists and turns, we give you 15 Things You Didn't Know About Law & Order: SVU.

These are their stories.

15. Richard Belzer’s John Munch is the Reigning King of Crossover

Richard Belzer as John Munch on Law & Order: SVU

In 2016, Richard Belzer returned to SVU after a two-season absence as Detective John Munch. Belzer, who'd been on the show from the beginning, left a few episodes into the 15th season, but the life of his character, John Munch, spans far beyond SVU. Munch originated on Homicide: Life on the Street, and he's traveled far and wide since then. He is the only character played by a single actor to appear on ten different TV shows, and his appearances have spanned across five different networks. His most notable appearances include stints on The X-Files, 30 Rock, The Wire, and Arrested Development.

To add to the fun, there has also been a Muppet version of John Munch, although he wasn't played by Belzer. Sesame Street included him in a sketch called Law & Order: Special Letters UnitHe even turned up in a comic book: Spider-Man/Deadpool #6.

When Belzer made his way back to SVU this past season, that officially marked John Munch's 23rd season on TV.

14. The Show Was Originally Called "Sex Crimes"

Law & Order: Special Victims Unit logo

For a long time, the show's working title was simply Sex Crimes. Not only did NBC struggle with this, anticipating trouble from both squeamish advertisers and sensitive viewers, they also realized that it was neither lurid nor a very apt description of the show. So they took the name of the real-life NYPD department that handled sexually based offenses, trading in sensationalism for legitimacy. They also got over their early qualms about attaching it to the L&O brand, deciding it would give the series a better chance of success.

Dick Wolf, creator of the Law & Order franchise, explained the title change back in 1999. “We’re going to be covering a wide range of crimes and “Special Victims unit’ just seems more inclusive,” he said. He also wanted to keep the show grounded in reality, somewhat; he'd gotten his original idea for the show from the famous murder case involving Robert Chambers and Jennifer Levin, about which he'd written a Law & Order episode. Still haunted by the case afterward, he decided to develop a show focusing on those types of crimes.

13. The Voice Actor in the Opening Served in Government Office

Steve Zirnkilton - SVU voiceover guy

"In the criminal justice system, sexually-based offenses are considered especially heinous. In New York City, the dedicated detectives who investigate these vicious felonies are members of an elite squad known as the Special Victims Unit. These are their stories."

This is how every episode of SVU begins, and like every other Law & Order show, the narration is voiced by Steve Zirnkilton. Zirnkilton was initially hired as a bit player in the L&O pilot, the only episode that he doesn't introduce. (He shared a trailer with William H. Macy during the shoot.) Dick Wolf ended up liking his voice so much that he made him a permanent part of the franchise. Zirnkilton has narrated other shows and even appeared on Family Guy and The Rugrats Movie, but an even more fascinating claim to fame is that he was also a politician. A Republican, he served four terms for a total of eight years in Maine's House of Representatives.

12. Mariska Hargitay is a Trained Rape Crisis Counselor

Mariska Hargitay as Olivia Benson in Law & Order: SVU

When Mariska Hargitay signed on to play Detective Olivia Benson, she had no idea how much the subject matter would affect her. The statistics alone were appalling, as they revealed that someone in the United States was sexually assaulted every two minutes. Deeply moved by letters from assault victims, she got trained as a rape crisis counselor, and then, in 2004, founded the Joyful Heart Foundation, which helps survivors of sexual assault, domestic violence, and child abuse through retreats, education, and advocacy.

She has also worked to change public policy. In 2010, she testified before a House judiciary subcommittee, talking about the backlog of hundreds of thousands of rape kits that have gone untested, a subject also covered in the show.

Hargitay has also learned how to spring into cop mode as needed. When a pregnant woman fainted on an NYC sidewalk, she ran to her side, shouting to passers-by: "Call 911, get her water!" and then started asking the woman questions that would help determine why she'd fainted. She walks the walk.

11. Ice-T Was Originally Only Hired for Four Episodes

Ice-T as Tutuola on Law & Order: SVU

Ice-T has been a thief, a drug dealer, a member of the U.S. Army, and a DJ, sometimes all at the same time. After being seriously hurt in a car accident, he traded in his less-than-altruistic for music.

His career as a rapper was both successful and controversial, particularly when he and his band Body Count released the song "Cop Killer." This was his biggest source of notoriety until he added acting to his résumé. Ice-T's first role for Dick Wolf was in the series New York Undercover, and Wolf later cast him as a pimp in a Law & Order TV movie.

When Dean Winters had to leave the show early on in SVU's run, Ice-T was brought in for four episodes as Detective Odafin "Fin" Tutuola. He gelled with the rest of the cast immediately, moved to New York before he'd even finished those four shows, and has been there ever since.

Ice-T said that when the show began, “Dick Wolf called me and was like, ‘Ice, you don’t like cops do you?’ And I was like, No, not really—not all of them.’ ‘But you admit we need them, right?’ ‘Yeah.’ [Wolf said], ‘Play the cop we need.’"

10. Mariska Hargitay is Fluent in Five Languages

Mariska Hargitay as Olivia Benson on Law & Order: SVU

You know all those scenes when Olivia Benson speaks to a victim or a perp in Spanish? She's not simply reading off a few memorized lines -- she's fluent in the language.

Hargitay's mother, Jayne Mansfield, was famous as a blonde bombshell, but there was more to her than that: she reportedly had an IQ of 149 (!) and spoke five different languages. Hargitay does the same, and besides English and Spanish, she's also fluent in Hungarian, French, and Italian. She's even given a tour of the SVU set to a Hungarian reporter in his native language.

She met her husband, actor Peter Hermann, on the SVU set when he guest-starred as defense attorney Trevor Langan, and they married in 2004. Hermann spent most of his childhood in Germany, and didn't learn to speak English until he was ten years old, so there are a lot of languages going around in the Hargitay-Hermann household. We assume their three children will be able to speak more than a few of them.

9. Hargitay & Meloni’s Chemistry was Instantaneous, even at Their Audition

Stabler and Benson on Law & Order: SVU

Chris Meloni and Mariska Hargitay met for the first time at their audition. The final casting call was down to three women (Hargitay, Reiko Aylesoworth, and Samantha Mathis) and three men (Meloni, Tim Matheson, and Nick Chinlund). Hargitay had heard that a friend-of-a-friend would be among them, so she walked in, saw Meloni, who she didn't know, and assumed that he was the guy. She shouted the actor's name, and Meloni stood up and shouted his own name instead, in fake recognition. Since she was already standing, they ended up in a huge hug, despite having never met before.

She noticed the big tattoo on his arm of Jesus on the cross, and asked, hopefully, if he was a Christian. When he said no, she asked why he had the tattoo. "Just liked his commitment," he told her.

They auditioned individually, and then the casting directors started pairing up the finalists. Hargitay crossed her fingers, and knew as soon as they said, "Mariska and Chris" that they were going to make magic. So did producers; as soon as the actors all left, no debate was needed. They'd found their stars.

8. Taylor Swift Named Her Cat After Olivia Benson

Taylor Swift still, staring at the camera

In June of 2014, Taylor Swift told fans via Instagram about her new kitten, who she'd named Olivia Benson. A huge fan of the show, she found herself at various events (like the annual Met Gala) with Mariska Hargitay, and took the opportunity, each time, to talk up how much she loved the show and the character of Olivia.

The two kept up a friendly relationship, and then one day they were at the same concert in Queens, when Hargitay and her husband realized they hadn't figured out a way to get home. So what happened? Swift offered them a ride, of course. (Doesn't this happen to everyone?)

The next stage in their friendship hit when Hargitay got a text from Swift asking if she wanted to appear in her new video, "Bad Blood." Of course she did! Hargitay has also gotten up on stage with Swift at her concerts, something that was a staple of the singer's "1989" tour.

7. Episode Titles Follow a Very Specific Pattern

Law & Order: Special Victims Unit cast season 13

Even though you never see them on screen, every episode of Law & Order: SVU has a distinct title, and for the first 18 seasons, they followed very specific patterns.

Season One was a little spotty, but near the end, they settled into a routine: all titles were just one word. This continued, with just a handful of exceptions, until the end of the twelfth season. That finale marked the departure of three actors: B.D. Wong, Tamara Tunie, and Chris Meloni, who of course had been one of the two headlining stars from the very first episode. Wong and Tunie have turned up from time to time, but Meloni hasn't been on the show since, and with such a drastic change came a new kind of episode title as well. From the 13th through the 17th season, episode titles became two words long, with the number of letters in them equaling the season they were in. Season 13 kicked off with "Scorched Earth" (13 letters), Season 14 with "Lost Reputation" (14), Season 15 with "Surrender Benson", 16 with "Girls Disappeared", and 17 with "Devil's Dissection."

In the 18th season, they gave up, and title rules went out the window.

6. Chris Meloni Got his Start in Commercials

Chris Meloni as Stabler on Law & Order: Special Victims Unit

Meloni originally went to college to study acting, but ended up earning a degree in history instead, then decided acting was right for him after all and moved to New York City to study with famous teacher Sanford Meisner. A former football player, he was already in great physical shape, so while he was still auditioning and struggling, he took jobs as a personal trainer, construction worker, and bouncer. When the chance to do commercials came along, he thought it was a much better option than bouncing, and jumped at the opportunity.

He did ads for McDonald's, as well as for some less famous companies.“You name it, bro, I advertised it,” he told an Irish newspaper. “Some of it was totally cheesy. I did this commercial in Germany for a washing machine repair guy. When the housewife takes the clothes out of the machine she goes: ‘Aii, Schmutzraender!’ [Oh no, stains!] And I look at her and repeat: ‘Aii, Schmutzraender!’ I went around Hamburg, trying to pick up chicks with this one lame phrase. Needless to say, I never got laid in Hamburg.”

5. Quite a Few Guest Stars are Also Oscar-Winners

Benson and Stabler arrest a robbery suspect

SVU, like all Law & Order shows, boasts some pretty impressive guest stars. Carol Burnett, Kyle MacLachlan, Sarah Paulson, Kal Penn, Norman Reedus and Viola Davis have all turned up, to name just a few. But even more prestigious is the fact that they've had so many Academy Award winners appear on the show.

Robin Williams played master manipulator Merritt Rook, who got other people to commit crimes for him, and recruited almost the entire population of Grand Central Station to help him hide from Benson and Stabler. He'd won his Oscar for Good Will Hunting ten years earlier.

Who else? Patricia Arquette (who won for Boyhood) played a kidnapped prostitute, and Dianne Wiest (Hannah and Her Sisters, Bullets Over Broadway) brought back her Law & Order character, District Attorney Nora Lewin. More Oscar-winning guest stars include Whoopi Goldberg, Olympia Dukakis, Jeremy Irons, Marlee Matlin, Marcia Gay Harden, Ellen Burstyn, and of course, there's J.K. Simmons, aka psychiatrist Emil Skoda, who won his Oscar in 2015 for Whiplash. There's also legend of stage and screen Angela Lansbury, winner of an Honorary Oscar in 2013 and guest star in an episode of SVU, along with Alfred Molina and a not-yet-famous actor Bradley Cooper.

SVU was never hurting for starpower.

4. The Catholic Church and the NFL have Given Producers the Biggest Headaches

Treat Williams on Law & Order: SVU "Spiraling Down"

Law & Order: Special Victims Unit has tackled some big issues, and taken on some pretty powerful organizations. Producers have talked about two in particular that pushed back.

During Warren Leight's tenure as showrunner from season 13 through 17, the show did two stories about NFL players. Leigh told E! News, "While the NFL was talking about how they were interested in championing victims of domestic violence, pressure was being applied for us not to do an episode about domestic violence." To Slate, he said“There is no bigger moneymaker for all network television, and we went there twice since I’ve been here...Nobody’s asked me to do a lot more of those, though.”

The second was the Catholic Church, which has come under fire for covering up systematic child abuse. SVU has done several episodes about the topic. Said Leight, "The Catholic Church, while they said they're going after predators, made their opinions clear. I wish in both cases those organizations were as quick on the draw against domestic violence or against predators in their midst as they are about bad publicity about those things. What they're exceptionally good at is keeping on top of anything that makes them look bad."

3. Chris Meloni's Double Duty on Oz & SVU Was Very Peculiar

Christopher Meloni on Oz and SVU

The crossover of actors between Oz and SVU makes for a long list. Dean Winters, B.D. Wong, J.K. Simmons, Lee Tergeson, Kathryn Erbe, Harold Perrineau, and Scott William Winters (Dean's brother) were all on both shows. But most notable was Chris Meloni, who was still doing Oz when he got the gig on SVU. He found working on both shows exhausting and gave up Oz for a while, then missed it and returned the following season. He described the experience of playing a sadistic rapist/murderer and a God-fearing, family man and detective at the same time in an episode of In The Actor's Studio, after explaining that for an actor, getting even one steady job was something to be grateful for. That said, it was challenging:

"It wasn’t easy. For about two of three years, I would wake up at 4:30, get in the van at 6, drive to Oz, kill people and sodomize them ‘til about noon, jump in the car, go to SVU, and go arrest people who murder and sodomize people ‘til about two a.m."

2. Mariska Hargitay Suffered a Partially Collapsed Lung on Set

Stabler and Bensen in Law & Order: SVU

Mariska Hargitay used to like to do her own stunts. "I'd always insisted on doing the stunts my own way, although I don't feel so strongly about that anymore," she told Redbook. She changed her mind after an incident in 2008 when she landed on pads during a stunt, but didn't feel quite right afterwards. She wondered if she'd pulled a muscle, and kept waiting for the injury to heal.

Two weeks later, she had chest pains and shortness of breath, and worried that she was having a heart attack until someone pointed out that her heart was on the other side. The pain became so severe that she couldn't catch her breath anymore, and finally got an X-ray, which is how she learned that she had a partially collapsed lung. She went back to work, and then months later, it happened again. This time she knew to get medical help.

Shockingly, the whole ordeal only caused her to miss filming a single episode of the show.

1. "Ripped From the Headlines" Isn't Quite What You Think

Gary Cole in promo from pulled SVU episode

SVU, like its predecessor Law & Order, has a reputation for featuring stories that are "ripped from the headlines." The Catholic League For Religious and Civil Rights even suggested alternative news stories for the show to cover when they were upset that abuse within the Catholic church was a story topic. But contrary to popular opinion, the expression is a lot looser than it seems.

What it really means is that stories are INSPIRED by headlines, that some element of something that's happening in the world will trigger an idea and the writers will fictionalize it from there. Sometimes it's just a single event, or a specific person, and then everything heads off in a completely different direction. They're not adapting news stories for the show, or even trying to match real-life events.

It still gets them in trouble. They shot an episode in 2016 called "Unstoppable" that was "inspired by" a real-life case around then-Presidential candidate (and now President-elect) Donald Trump and the sexual assault accusations made against him by multiple women. The episode, which starred Gary Cole as the Trump-esque candidate, was delayed a few times before the election, and once Trump won, it was taken off the schedule entirely.

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SVU is currently in its 18th season, and while Chris Meloni isn't on the show anymore, he's still tight with former co-star Mariska Hargitay. She's the godmother to one of his children, and they recently got together and posted a selfie on Instagram, making fans drool at the possibility that Stabler might one day make his way back to the show. Fingers crossed!

Law & Order: SVU returns with new episodes on Wednesday, Jan. 4 at 9 p.m. on NBC.