Superhero films have definitely grown in popularity in the past decade. Why not? More often than not, they're rousing and intriguing, so we look forward to them. The hundreds of millions of dollars they earn in box office revenue can attest to that. Still, there are potentially great films (or rather, concepts) that just can't seem to make out of that dreaded development hell and there are dozens of superhero films among them, trapped there for a variety of reasons.

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We've compiled a list of 15 such superhero films to keep hope alive if nothing else. "Deadpool" proved to us that there is hope, even in the depths of development hell. Maybe we'll see at least one of these films completed one day.

15 GAMBIT

Gambit-New-Orleans

Fans have been wanting a proper Gambit appearance in the "X-Men" films since his name first appeared in "X2: X-Men United" (directed by Bryan Singer) way back in 2003. A solo film has been stuck in its initial stages since 2009. Back then Taylor Kitsch was attached to the film, having already played Gambit in "X-Men Origins: Wolverine" (directed by Gavin Hood). Producer Lauren Shuler Donner would later state that Channing Tatum would be playing the titular character instead. That was in 2014 and since then, there hasn't been much in the way of development.

The script is supposedly being re-written (or so the rumors go) yet again, and directors like Rupert Wyatt and Doug Liman have come and gone, so right now it seems like it's still pretty much just a concept. It'll be a long time until we see "Gambit" in theatres. Simon Kinberg, a producer and writer, said just as much when discussing the film with "Variety" back in 2016, likening it to "Deadpool," which took about 10 years to get out of development hell. Let's hope we don't have to wait that long.

14 THE SANDMAN

The Sandman

Neil Gaiman's "The Sandman" was a comic book series that ran from 1989 to 1996. It follows Dream, also known as Morpheus. After escaping his imprisonment, Dream begins rebuilding a kingdom while embarking on a redemptive path. This award-winning comic series is just begging to be turned into a film. Since the 90s', directors have been attached and scripts have been written, none have been good enough for Neil Gaiman who would prefer no "Sandman" film to a badly written one. How can anyone disagree with that?

The last screenwriter to leave, Eric Heisserer, said that "The Sandman" shouldn't be a film but a TV series, and why not? Right now, there's already "Lucifer" which was adapted from the character in "The Sandman." TV shows are getting bigger and better and there's a lot of potential there for an adaption of that scale. For now however, like Gaiman's character, it's all just a dream.

13 LOBO

Lobo-finch

Lobo is a lot like the Deadpool of DC Comics. He's an anti-hero who loves violence and blood, originally created as a parody of Marvel characters such as the Punisher and Wolverine. He became quite popular and has appeared in numerous comics and cartoons.

Let's be fair: it'd be pretty easy to get a film about a motorcycle-riding alien bounty hunter incredibly wrong. The concept of a "Lobo" film has been floating around since 2009 at least. There was a plot involving four bad guys and a small-town girl and Guy Ritchie was meant to direct. Unfortunately, Ritchie left to complete the "Sherlock Holmes: A Game of Shadows" film. Two years later, Brad Peyton was attached as director with talks of Dwayne "The Rock" Johnson starring as Lobo (given that he'll be playing Black Adam, that probably won't be happening anymore). Not much else has been released about the status of that film, leaving it in the murky depths of development hell.

12 NAMOR THE SUB-MARINER

namor-the-sub-mariner

Namor is quite a prominent character in the Marvel Comics universe, so as king of Atlantis, he deserves a film. Back in 2002, a film was actually in development. Director Chris Columbus was attached, then Jonathan Mostow replaced him, then nobody was attached. With all the excitement surrounding the ever-expanding Marvel Cinematic Universe, you might be wondering why Marvel doesn't just include the Sub-Mariner.

They don't exactly own the film rights to the Sub-Mariner. Though Marvel Editor-in-Chief, Joe Quesada, did say that rights had reverted back to Marvel in 2016, Kevin Feige, president of Marvel Studios, explained that it wasn't that simple. Marvel got the rights back from Universal Studios, however, there are still "other parties involved" (according to Feige) resulting in quite the tangled situation, one people are understandably hesitant to tackle.

11 WITCHBLADE

witchblade-series

Beginning in 1995, "Witchblade" was a comic book series that centered on Sara Pezzini, an N.Y.C. detective to whom the mystical Witchblade bonded. The gauntlet gave her powers such as supernatural strength, the ability to form a variety of weapons and bring things back from the dead. There was a TV show adaptation that ran from 2001 to 2002 and a made-for-television pilot film that preceded it, but nothing close to the superhero films we have today.

The idea for a big budget "Witchblade" film has been around since at least 2008 when one was announced with many of the producers behind the TV show attached. Unfortunately, it was just never produced. There was talk about a film about the Darkness, one of the primordial forces behind the Witchblade. In that film, the Witchblade would make an appearance, however nothing has yet come of that either, and it seems both have been condemned to development hell.

10 THUNDERBOLTS

Thunderbolts

The Thunderbolts are a team of reformed villains led by Baron Zemo. They're not as big as other hero groups like the Avengers or the Guardians of the Galaxy, which is perhaps why they've only appeared a handful of times outside of comics books, including in episodes of "Ultimate Spider-Man" and "Avengers Assemble." Those adaptations have been more or less faithful to the comic book source material and were pretty well received, at least by the young demographic they were aimed at.

Before "Guardians of the Galaxy" (directed by James Gunn), it seemed as though "Thunderbolts" would actually get made, with Gunn directing. Unfortunately for "Thunderbolts," the overwhelming success of "Guardians of the Galaxy" meant that it would have to be put aside, at least for the time being. Don't get your hopes up for seeing them included in the MCU anytime soon. This is one film in development hell that's evidently intentionally being kept there.

9 THE INCREDIBLE HULK 2

Incredible-Hulk

Currently the only MCU movie to not have a sequel is 2008s' "The Incredible Hulk" (directed by Louis Leterrier) and it seems as though, with Mark Ruffalo having just four more films on his contract, that chances of that sequel happening are getting slimmer. While this might be for the best since "The Incredible Hulk" wasn't exactly the most well-received film out of the Phase 1 block, it may not be the entire reason for the absence of a sequel.

Universal Studios had both the production rights and distribution rights to "Hulk" films, however the production rights reverted back to Marvel in 2008 while the distribution rights (which were open-ended) remain with Universal, which is why you'll still see the Hulk in other superhero films like "The Avengers" or the upcoming "Thor: Ragnarok" but not his own. It'll be a while before the incredible Hulk gets another film of his own, unless a deal is made between Marvel and Universal, a bit like the one they have with Sony that allowed "Spider-Man: Homecoming" to be made.

8 KICK-ASS 3

Kick-Ass

Some might wonder why no one bothered completing the "Kick-Ass" trilogy, especially after Mark Millar announced plans for a third instalment while "Kick-Ass 2" (directed by Jeff Wadlow) was still in production. The simple answer is: because the last one didn't make that much money. From its budget of $28 million, "Kick-Ass 2" made just $60 million at the box office (lower than its predecessor) and the critical response was less than ideal. That's apparently what's been keeping Matthew Vaughn from giving the go-ahead on the last in a potential trilogy.

Instead, Vaughn seems intent on creating a prequel focusing on Hit-Girl before going ahead with any plans on the third "Kick-Ass" film, confident that he can persuade Chloë Grace Moretz to return after she said that she was done with her Hit-Girl character. It's been a while since Vaughn stated that (back in 2015) with no news on new development. Only time will tell if "Kick-Ass 3" will ever hit theatres.

7 BATMAN BEYOND

batman-beyond-costume-terry-mcginnis

This fantastic series did an incredible job at expanding on Bruce Wayne's life, giving him a retirement worthy of the Batman. There were plans to develop a film back in 2000, with a script being drafted. Like the series, it was set in the future with a young Terry McGinnis under the tutelage of Bruce Wayne. Even Ace was going to appear in the film. Unfortunately, the commercial failure of Joel Schumacher's "Batman" films meant no one was going to touch the property so, nothing came of it. Instead, "Batman Begins" was born.

Right now, there are nothing but rumors surrounding it started by fans who still hold hope that "Batman Beyond" will still get made. With all these superhero films coming out, there is still a chance. A futuristic film about a futuristic Batman? Sounds good. Maybe one day in the not-too-distant future, someone in the industry will see value in "Batman Beyond" and take on that project.

6 BLADE 4

Blade pulls out his katana from behind his back from the 1998 film

The "Blade" trilogy ended terribly. Aside from the critical failure of the film, Wesley Snipes had a falling out with New Line Cinemas and director David S. Goyer, claiming that they didn't pay him his full salary and that he was cut out of decisions despite being a producer. With the mess, anyone could see that a fourth film was pretty unlikely. It wasn't long before New Line Cinema lost the rights to the film, having failed to produce anything with Blade after that third film.

Film rights to Blade reverted back to Marvel in August 2012, but as of yet, Marvel understandably has no plans for the property. Although, Wesley Snipes has stated that there have been discussions about making another film and he made it clear that he's interested in playing Blade again if a reboot ever does happen. Blade is something Snipes is known for and it might be difficult to recreate Blade to fit in with the rest of the MCU.

5 SPAWN 2

Spawn

Spawn, created by Todd McFarlane, has a long-running comic series that began in 1992. It follows Al Simmons, former marine, brought back from the depths of Hell as a powerful pawn to be used in the war between Hell and Heaven. It sounds like it would make for an epic film, unfortunately, "Spawn" (directed by Mark A.Z. Dippe) was less than satisfactory, to say the least. A sequel was never made, though Todd McFarlane seems vehement in his pursuit of making another Spawn movie.

McFarlane has described his vision of a Spawn reboot as something more akin to the comics. He's said that his new film, for which a screenplay has already been written, will not have a supervillain. Both Michael Jai White, who played Spawn in the 1997 film, as well as Jamie Foxx, have expressed interest in playing the titular character in the reboot. In 2016, MacFarlane stated that the script has been written, it just needs editing, which means there may be hope for this film yet.

4 BLACK WIDOW

Black Widow

Even before the Marvel Cinematic Universe took off, there were talks of Black Widow getting her own movie. In 2004, David Hayter was commissioned by Lionsgate Studios to write a script, but he later dropped out. It was said that in 2010, the studio was in talks with Scarlett Johansson about a solo film. However, nothing came of it. Johansson still seems very enthusiastic about a solo film, saying "you could bring it back to Russia. You could explore the Black Widow program. There's all kinds of stuff you could do with it."

Both Johansson and Kevin Feige have said that there's a good chance the solo film could start production after "Avengers: Infinity War" is done. He's gone so far as to say that there's potential for a standalone franchise focused on Black Widow. That's all well and good, but no reason to get excited. For now, that Black Widow film remains somewhere on the shelves in Hollywood.

3 NICK FURY

Nick Fury

We've come a long way since David Hasselhoff played Fury in "Nick Fury: Agent of S.H.I.E.L.D" back in 1998. Since then, the head of S.H.I.E.L.D is yet another character that has been somewhat neglected. He was supposed to have his own film as part of the first phase of the MCU. A screenplay was written by Andrew Marlowe, but then nothing more happened.

Samuel L. Jackson did have nine films in his contract, meaning he's got two movies left. There are rumors that he'll appear in "Captain Marvel" but there's nothing solid on that yet. All we've got is maybes and ifs. There's still that script, so maybe they'll choose to do something with it, maybe Samuel L. Jackson will have his own film after "Avengers: Infinity War." There's an abundance of rumors, most of which stem from a single interview in which he stated that he might be "Captain Marvel" before uttering something about Fury searching for the Red Skull. Interesting stuff, but again, nothing concrete. For now, the Nick Fury solo film is stuck down in the back of everyone's mind.

2 NEMESIS

7-NEMESIS

Matt Anderson was an affluent kid who lost his father after he committed suicide thanks to Officer Morrow. Matt travelled the world, developing incredible skills he would use for...evil! As described by Mark Millar, Nemesis is basically Batman if Batman were the Joker. The four-issue "Nemesis" series (written by Millar, illustrated by Steven McNiven) had a mixed reception at best. Nevertheless, plans were made to adapt it to film in 2010 with the involvement of 20th Century Fox, Tony Scott as director and Joe Carnahan as screenwriter.

It's been a long road however. After Tony Scott passed away, Carnahan was made director with his brother, Matthew, aiding in writing the screenplay. There wasn't much news afterwards until later in 2015 when it was announced that Warner Bros. would adapt the film instead. Still not much news, so it's doubtful we'll be seeing a "Nemesis" film anytime soon, despite being told it'd start filming depending on the success of "Kingsman: The Secret Service" (directed by Matthew Vaughn), based on Millar's comic book of the same name.

1 THE CROW (REBOOT)

The Crow

"The Crow" (directed by Alex Proyas) has gathered a cult following since its release in 1994. The film, centered on Eric Draven, a rockstar who returns from the dead to avenge the death and rape of his fiancee. It was a commercial and critical success, though its sequels were definitely not up to standard. In 2008 came news that Stephen Norrington planned to reboot the series. As it developed, it became clear that it would remain faithful to the comics.

James O'Barr is currently attached as a consultant and, after a series of legal battles over the film fights, we've been told time and time again that filming will begin soon, with different stars and directors. More recently, Jason Mamoa has been attached to star as Eric, but with Relativity Media dealing with its own financial troubles, that might change with contract renegotiations and possible scheduling conflicts. Maybe it just isn't meant to be.

Which superhero movies that never finished getting developed were you looking forward to seeing? Be sure to tell us in the comments!