Three hundred thirty-one episodes. One hundred twenty-four Emmy nominations. Forty-nine million viewers. One George Clooney.

Thirty years ago, ER debuted on NBC, introducing viewers to the emergency room doctors at County General Hospital in Chicago. The medical drama would launch the careers of Clooney, Noah Wyle and Julianna Margulies and run for 15 seasons, making it the second longest running medical drama in TV history. 

When it premiered Sept. 19, 1994, ER—which starred Top Gun star Anthony Edwards, Sherry Stringfield and Eriq La Salle—was actually an underdog, with most industry insiders assuming CBS' Chicago Hope would win the battle of the big medical procedural.

Still, ER ended up becoming the No. 1 show on TV, almost hitting 50 million viewers at one point. As it continued, airing over 300 episodes before ending in 2009, actors like Maura Tierney, John Stamos, Linda Cardellini and Goran Visnjic joined the ensemble.

Back when ER first debuted, Clooney gushed about his newfound stardom in an interview with E! News.

"It's fun, are you kidding?" the Oscar winner raved. "You spend your whole life, your whole career, trying to get on a show like this, that people pay attention to and they put you on Newsweek and stuff. It's a dream come true, it's fun for us, you know. It's tiring just because of our hours on this show, you know, are so long—that we're a little beat and then they say, 'OK, let's go do a photo shoot.' But it's be careful what you wish for you know? But we're having the time of our lives, it's fun."

While Clooney left the show after five seasons, he made several return appearances and has often spoken fondly of his experience on the show...one he actually had to beg to be cast on.

That's just one secrets executive producer and showrunner John Wells and several of the series' stars have revealed over the years, with others including squashed storylines, on-set pranks and ER's most devastating deaths.

No need to page us for all the details. Keep reading for more ER shockers in honor of the 30th anniversary.

1. ER was initially intended to be a movie back in 1974, with Steven Spielberg set to direct a script penned by Michael Crichton, which would be "a documentary-style movie about what happened during 24 hours in an emergency room" based on his experience as a med student in Boston. Alas, it never ended up happening, with the project shelved for almost 20 years before NBC expressed interest in making it a TV series. 

2. While Carol would go onto become one of the show's most beloved characters, she was never intended to be in any episodes beyond the pilot, as the original script had Margulies' character dying. But after test audiences responded well to the nurse, a dubbed line was added in to explain how she survived her suicide attempt. 

3. But Margulies has since revealed it was actually Clooney who "saved" her career by convincing her to stay on ER and not join a CBS sitcom that was courting her, with The Good Wife star explaining, "He called me out of the blue, kinda put his neck out on the line for me, and said, 'I overheard that your character tested well...If I were you, I wouldn't take another job because I think they're going to bring you back to life."

4. While it became the No. 1 show on TV, the medical drama initially didn't test well, causing cause for concern at NBC after the first screening. "When the lights came up, it was not a very positive reaction," Kevin Reilly, who was the VP of development at NBC at the time, told EW. Execs were concerned over the gore and medical jargon, believing it had too much action and too many characters for viewers to handle. Of course, they were wrong, with Wells saying their issues were "all the things that ended up becoming the hallmarks of the series." 

5. It might be hard to believe, but back in 1995, a 33-year-old Clooney actually "begged" for a part on the show, according to Wells. "Our second day in the office, George showed up and wouldn't leave until I'd let him audition," Wells recalled. "George got his hands on the material and was like a dog with a bone."

6. One romance that was nixed early on was the one between Benton (La Salle) and Dr. Corday (Alex Kingston), after Benton expressed concern over the message their interracial relationship would send after his previous romances with black women had all been depicted.

"As an African American man, it becomes a bit offensive if the negative things are all you're showing," the actor explained. "Because in real life, we romance and get on each other's nerves and laugh and do all the things that any other race of people do."

7. A lot of pranks on set, with Edwards telling People the cast was "always laughing," A classic prank was putting Vaseline on phones before a co-star had to do scene using it, and his favorite one was pulled on a guest actress.

"When she gave birth and we'd been bringing up this fake baby, we brought up the alien baby," he said. "I never heard someone scream as loud as she did at this green baby."

8. The only storyline Wyle asked to be squashed in his 254-episode (the record) tenure? A sex scene between Carter and Lucy, his student, with Wyle telling EW, " I had such a huge problem with it. The script originally had us having sex in one of the exam rooms, and somebody walking in on us. I had a big problem with it." Explaining he viewed the character as "his little sister," he asked Wells to change the script, with the two kissing just once, despite fans shipping the couple. 

9. Looking back, Wyle admitted he wasn't exactly the most welcoming co-star when Martin joined the show in season five, revealing to EW, "Here's where I harbor a lot of guilt. I was not nice all the time to Kellie. We worked extremely hard to be the No. 1 show over those five seasons, and when Kellie came on, or whenever anybody came on, it was like, 'Earn your keep!'"

10. In season six, ER shocked America when it killed off Lucy in brutal fashion, with a schizophrenic patient slitting her throat before going on to stab Carter (who survived the attack). "John Wells called me into his office, and we had a discussion about them wanting to do something big with Lucy, and have her leave the show," Martin explained to EW, "I was 21 or 22. I remember taking it kind of personally that I was being stabbed and leaving the show. I was definitely traumatized." So were the 30 million viewers who tuned in.

11. David Krumholtz played the patient responsible for killing one of America's sweethearts and is still dealing with the fallout years later, revealing to EW, "I still get messages on Twitter now that people have never fully forgiven me for what I did."

12. After seasons of having Laura Innes walk with a fake hip, the writers had Dr. Weaver had to undergo hip surgery in season 11 because their star had developed back problems due to playing the character. "My real back was getting screwed up," she revealed. "I got a bone density test and the bottom of my spine is starting to curve on one side from ten years of raising my hip."

13. After fulfilling his five-year contract, Clooney, then a full-blown movie star, left the series under good terms, with Wells once saying the actor had "lost literally millions of dollars by staying on the show."

14. Clooney made a surprise return the following season for Margulies' final episode, which was kept so secretive that the network didn't even know it was happening. "It was never in any scripts. [NBC] knew nothing about it. Then I processed [the film] two or three days before it was on the air, and we cut [the scene] in very late at night when nobody was around," Wells told EW, noting the network didn't see Clooney's scene until it aired on the east coast. (Much to their chagrin, given the potential ad sales boost they lost out on.) 

After it aired, Clooney said, "People were going bats--t over the idea that we'd pulled it off." To do so, Warner Bros. chartered a private jet to fly Clooney and a few small crew to Seattle, with everyone involved signing pledges. 

15. The last of the remaining original cast members, Wyle left the show in season 11 after the birth of his son, Owen, reflecting to THR, "I just thought, I can't be here for 80 hours a week and miss this. And I quit." He ended up returning for six episodes of the 15th and final season, explaining it was "so great. Talk about closure. To not be on that show and have that show be on TV was horrible."

16. While it wasn't technically a crossover event as they weren't playing their ER characters, Clooney and Wyle played doctors in a season one episode of Friends, another NBC newbie that was debuting that same year. In the episode, their characters go on a double-date with Monica (Courteney Cox) and Rachel (Jennifer Aniston). 

17. After joining the show in season six as Dr. Abby Lockhart and quickly becoming a fan-favorite and the show's eventual female lead, Maura Tierney left at the beginning of the final season, saying in an interview, "I want them to kill me...and they won't. They refused to kill Abby." They didn't and years later Tierney said she was happy they didn't, as she loved Abby's final arc: "I got to go out with a bang," she told The A.V. Club. 

18. After ratings were steadily declining for several seasons, ER briefly saw a second life when John Stamos joined as a series regular in season 13 as Dr. Tony Gates. The Full House star revealed that he actually decided to join the show full-time after randomly running into Clooney. "I haven't told many people this. I was at lunch. I wasn't at lunch with him, but we were sitting and he said, 'You should go and do ER,'" he told Extra. "He was the one who told me to go on ER." Stamos would later call ER his "favorite job ever."

19. ER became a surprising source of health information for viewers, with a 2002 study (conducted by Kaiser Family Foundation) revealing a third of viewers said the show had helped them make health care choices and found it had increased their knowledge of medical conditions and terms after watching episodes featuring those subjects. In a 2001 study, one in five doctors said a patient had used ER as a reference point in a consultation. 

20. After he spent eight seasons on the show, fans were shocked when Dr. Greg Pratt died in the beginning of the final season, with Mekhi Phifer revealing people still come up to him about his character's death. And it turns out, he helped come up with the idea, sitting down with the producers ahead of the final season to come up with his dramatic end. "I'd rather him go out with a bang," the 8 Mile star told The A.V. Club. 

21. After Clooney starred in his film From Dusk Til Dawn, Quentin Tarantino directed an episode of ER in its first season. He reportedly netted $30,000 for the gig, which came just two months after he won the Oscar for writing Pulp Fiction. 

22. At one point, ER was one of the most expensive shows on TV to make, costing $13 million per episode. But it was also one of the highest rated shows ever, reaching its peak in 1998 with 47.8 million viewers. 

23. After ER's 15 season catalog became available to stream in 2018, E! News learned 35,000 viewers finished all of the episodes in just over two months--that's 240 hours of TV consumed, with viewers watching an average of five episodes per day. Plus, 90 percent of viewers started from the very beginning and the common age of the viewer streaming ER in the first week it was available was 27.

24. So any chances of a revival? Well, Clooney didn't exactly say no when we asked him about it at a press event in 2019, with the charming superstar saying, "Do you think that's a good idea? I'd play a patient now!" And the fact that Grey's Anatomy recently beat out ER to become the longest running medical drama on TV might help persuade him, as Clooney joked, "That's got to stop. We gotta go back and do some more!" 

25. But really, what are the odds, you might wonder. Wells didn't inspire much confidence when he told Deadline, "We made an awful lot of ERs, 331 episodes. That's a lot of hours, so I can't imagine that we would, but if somebody came in with a really interesting idea about how to do it, we might."

This story was originally published Sept. 19, 2019 at 3:00 AM PST.