Netflix TV series Stranger Things became the surprise hit of the summer. A unique blend of horror and science fiction with teen sensibilities, the show was nostalgically retro with its setting in 1983. In the fictional town of Hawkins, Indiana, the show was about a group of three boys who discovered that their missing friend, who was abducted by a terrifying monster, and a new girl in town with psychic powers were somehow connected. The show was compared favorably to 1980s movies like Stand By Me and The Thing, but with its own modern twist on the genre.

RELATED: The Upside Dank: 16 Stranger Things Memes

Finally, the show has returned with October's Stranger Things 2 taking us back to Hawkins again. The second season has answered all sorts of questions like what happened to Eleven, and what effect the Upside Down had on Will Byers, but some of the most interesting things happened behind the scenes. The journey from a controversial idea by the Duffer Brothers to the final shows that aired was anything but smooth, and there are some mysteries that came along the way. CBR is here to give you the inside story on 15 things you never knew about the first season of Stranger Things.

Warning: This article will have spoilers for Stranger Things and Stranger Things 2.

16 THE DUFFER BROTHERS' FIRST TV SHOW

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Stranger Things was created by Matt Duffer and Ross Duffer, writer-director twins who work together as the Duffer Brothers. Having a hit TV show is a great accomplishment for anyone, but more so for the Duffer Brothers considering their background. The two aren't seasoned veterans in Hollywood with a long list of accomplishments in IMDB. In fact, they only started working in Hollywood six years ago and have made exactly one movie and no TV shows before Stranger Things.

Their only movie credit is Hidden, a 2015 horror movie they wrote and directed about a family hiding in a fallout shelter during a viral outbreak. The movie wasn't very successful, but it got the attention of M. Night Shyamalan, who hired them to write and produce episodes of his TV show, Wayward Pines. It was their experience on Wayward Pines that led them to create Stranger Things.

15 IT STARTED WITH A KIDNAPPED CHILD

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According to the Duffer Brothers, the idea for Stranger Things came from the 2013 movie, Prisoners. The film about a desperate father who kidnaps and tortures a man suspected of taking his missing daughter captured the Duffers' imagination. They thought it was too short, and believed a TV show about the grief and angst of a parent searching for their missing child could be great.

As they brainstormed ideas for the show, the concept of throwing a cannibalistic monster into the mix came to them and they loved it. The monster started to take over the story as they imagined how it would get there and where it came from. They wanted to do a science fiction origin instead of a supernatural one, leading them to have the creature from another dimension. The Upside-Down and Eleven were born.

14 EVERYONE HATED IT

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Stranger Things is a monster hit (pun intended) for Netflix, so it's hard to believe right now, but the Duffer Brothers had a hard time selling their concept for the show. In fact, they estimate that as many as 15-20 networks turned them down when they pitched the show.

Apparently, one of the sticking points with the show was that the Duffers wanted to make the show centered around a group of children, but didn't want it to be a children's show. Networks thought that children would find it too scary, and that adults would be turned off by the underage leads. Some executives tried to convince the Duffer Brothers to either make the show more kid-friendly or get rid of the kids and focus on Chief Hopper's investigation.

13 IT LOVES THE '80S

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If there are elements of Stranger Things that seem familiar to you, it's not an accident. The Duffer Brothers decided to set the show in the '80s because of their love of old movies and TV shows. The show is set in 1983, because that was the year before Red Dawn came out at the height of Cold War paranoia.

The idea of a little girl with incredible psychic powers came from Stephen King's Firestarter, as well as King's Stand By Me. It also inspired the concept of following a group of children who bond over incredible circumstances. The monster draws from movies like Alien and The Thing while some shots in the first season were based on shots from E.T. However, the show also draws influences from modern references such as the town in the horror video game Silent Hill.

12 RETRO FOR THE DUFFERS

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With all the references to the era, it's easy to think that Stranger Things is a show made by and for children of the '80s, but while the latter might be true, the former isn't. The Duffer Brothers were actually born in 1983, so they were too young to remember what life was like in that year. By the time they started first grade, the 1980s were almost over.

Yet the Duffers have said they identified with the era because of their vast collection of videotapes growing up, most of which seem to have been from the '80s. They also didn't have cell phones, computers or Internet in the '90s, so they identified with the older years. Then there's the fact that Stephen Spielberg and Stephen King's movies hit their peak in the '80s, and the Duffers dreamed of making their version of those classics.

11 THE SHOW WAS CALLED MONTAUK

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Stranger Things changed a lot between the first pitch and the first episode, and that starts with the name. The series was originally called Montauk, and it was set in the real town of Montauk, New Jersey. Montauk holds a special place for horror fans, because the novel (and movie) Jaws was inspired by the gigantic shark caught by a Montauk fisherman.

Yet when the Duffers decided to set the series in a fictional town that would give them more freedom, they were forced to come up with a new name for the show. The brothers worked with Ted Sarandos at Netflix to come up with ideas, and while it would be great to say they came up with Stranger Things immediately and loved it, they didn't. In fact, they didn't like the title at first and had many arguments before settling on it.

10 SEASON 2 CAME FIRST

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When the show went into production, Netflix knew it had a massive hit on their hands, but there was a problem. The Duffer Brothers originally wanted Stranger Things to be a miniseries with a definite ending: the death of Eleven. In the season one finale, Eleven disappeared along with the Demogorgon, and that was supposed to be the end of the story. Netflix changed the minds of the Duffer Brothers to expand the story for the second season and beyond.

The brothers came up with a storyline for the next season and Netflix greenlit the new episodes before the first season even aired. However, the brothers were coy in interviews, claiming not to know if there would be a season two to build more anticipation when they finally announced it.

9 THE PROPS ARE REAL

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Stranger Things has been praised for its authenticity to the time period. Everything from the clothes to the hair to the toys they use seems plucked right from the '80s, and that's because they really are. Many of the things we saw on the show were actual items from the 1980s, like the Trapper Keepers and toys in the kids' rooms.

The costume and prop designer spent a lot of time and money on eBay gathering up things from the period to feature on the show. One exceptional item was a toy model of the Millennium Falcon that's featured in one episode straight from Lucasfilm (although it's not the original toy, because the 1980s Millennium Falcon toy had stickers instead of light-up engines). One of the few things that the show had to make custom are the kids' clothes because they were still growing during filming.

8 THE CAST SHAPED THE SHOW

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When it came to casting Stranger Things, there was a daunting task of hiring four extraordinary children to play the lead roles. Anyone who's worked with children in Hollywood knows they can be a challenge, and it's even harder to find children to carry the deep emotional requirements of the roles in Stranger Things. That's why the casting process started early with the Duffer Brothers auditioning thousands of children before selecting the four who came to form the cast.

Once the characters were cast, the writing began with story changing to reflect the mannerisms, look and strengths of the actors. For instance, the nerdy Dustin Henderson has cleidocranial dysplasia which left him with his baby teeth and a pronounced lisp. The condition was never part of the original character, but the actor Gaten Matarazzo has it in real-life and the character was written to accommodate it.

7 SHE WENT TO ELEVEN

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One cast member should be singled out, Millie Bobby Brown who plays the psychic powerhouse known as Eleven. The Duffer Brothers were inspired to create her by the real-life CIA experiments called MK-ULTRA, the destructive psychic girl in the anime Elfen Lied and the lovable alien in E.T. The series found Eleven's role the hardest to cast because it required a child who could act and show emotion without a lot of dialogue. It also needed a girl to shave her head, which turned out to be something a lot of actresses refused to do.

When Millie Bobby Brown auditioned, they thought they had their girl, but she showed the same hesitation about shaving her head. In desperation, the Duffers showed her pictures of Charlize Theron's character Furiosa in Mad Max: Fury Road to show how cool she could be. Fortunately for all of us, Brown agreed.

6 THE SHORT SEASON

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One of the toughest things for fans of the show is that there are so few episodes: eight the first season and nine the second season. While many TV shows like Game of Thrones struggled to get the entire story onto the screen in so few episodes, Stranger Things is a rare exception. The Duffer Brothers like it that way.

When the brothers originally pitched the show, they wanted to do it as a miniseries but network executives wanted a traditional 22-episode season. The Duffers weren't sure they could stretch the story out that long, but Netflix agreed to let them do only eight episodes. It was cheaper for Netflix, and the Duffers felt like eight episodes was a perfect length to let them delve into the characters and mystery in equal amounts.

5 THEY WANTED LESS CGI

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One of the things that the Duffer Brothers wanted to do in Stranger Things was use more physical (also known as "practical") special effects. Going back to their love of movies from the '80s, the Duffers felt that computer-generated special effects weren't as effective as practical effects, and referenced J.J. Abrams use of real props in Star Wars: The Force Awakens on how they wanted to blend real and CGI effects.

Unfortunately, they weren't able to do as much as they wanted. The brothers estimate that about 50% of the effects on the show were CGI, even though their original goal was 20%. With the short shooting schedule, they couldn't pull off some effects like the Demogorgon smashing through walls practically, so they had to resort to using CGI.

4 JUSTICE FOR BARB

One of the biggest surprises in Stranger Things was a minor character, Barbara Holland. Better known as Barb, Nancy's classmate served as a voice of reason who was killed by the Demogorgon early in the show. Yet her brief appearance and lack of impact on the rest of the story made her a heroine whose "Justice for Barb" campaign divided the fandom.

The Duffer Brothers admitted later that they also felt a kinship for Barb when writing her, and felt bad that they couldn't dig deeper into her death because the disappearance of Will Byers had to be the focus. The actress Shannon Purser also brought a surprising depth to the role, standing out as an outsider among the cast. This was actually Purser's first acting role, but it made a big impact. So many fans flooded her day job at a movie theater that she had to quit.

3 THE DUFFER BROTHERS' MONSTER

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The Duffer Brothers have said they've always wanted to make their own monster on the screen, and they succeeded with the horrifying interdimensional monster in Stranger Things. Nicknamed the Demogorgon, the monster was a carnivorous creature with the power to enter our world, snatch away its victims, and vanish back into the Upside Down.

The Duffer Brothers have said the creature was inspired by Guillermo del Toro's monsters from Pan's Labyrinth and H.R. Giger's Xenomorph in Alien, creatures with a grotesque human look. The breakthrough in the design came when they came up with the idea of it having no face, but head that opened like a flower. The brothers wanted a man in a suit, so most of the Demogorgon's appearances were played by an actor in a costume, but CGI was used for difficult scenes.

2 BEHIND THE UPSIDE DOWN

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In the first season, there was very little explanation behind the Demogorgon and the Upside Down. We knew the Upside Down was an alternate dimension, a dark reflection of our own. We knew the Demogorgon was a creature that came to our world to feed on meat. It could have been an X-Files situation, where the show just did weirdness for the sake of weird with no plan, but that's not what happened.

As seen in the second season, the Duffer Brothers knew more than they revealed. They actually wrote a 30-page secret document that explained the Upside Down and the Demogorgon, but decided to hold back the information to focus on the storyline of the first season. In the second season, we learned about the Demo-dogs and the Mind Flayer and there may be more to come.

1 STEVE WAS A BULLY

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When you create a TV show, a lot can change between the time you write the first script up to the time you're done shooting, and that's true in the case of Stranger Things. Many of the characters changed when the actual actors were cast, and their performance defined their character arc. That was the case with Steve Harrington.

In the original concept, Steve was your typical sex-crazed bully seen in '80s movies who got his comeuppance in the end. That all changed when Joe Keery was cast. Keery was such a charismatic actor that the Duffer Brothers decided to build a story arc to have him go from villain to hero. The brothers also decided to throw off fan expectations by having Nancy go back to Steve instead of Jonathan Byers in the first season finale.

What did you think of Stranger Things? Let us know in the comments!