At the 2017 D23 Expo, Mark Ruffalo revealed to fans that he a solo Hulk movie will never happen. According to him, Universal studios still has the rights to it, and they aren't interested in playing nice. Obviously, this was disappointing news to many fans. The Hulk has been a part of the Marvel Cinematic Universe since the very beginning, with The Incredible Hulk (2008) being the second movie in the series. Of course, that film starred Edward Norton in the title role, and Mark Ruffalo didn't step in until The Avengers in 2012. Ruffalo's take on the hero, however, has been widely praised and is hugely popular among audiences. Despite the somewhat lackluster response to The Incredible Hulk, a new movie starring Ruffalo's take on the character is often considered to be a surefire hit.

RELATED: Thor Ragnarok: 10 Things We Know (And 5 Rumors We Hope Are True)

While that's the common belief, it might actually be for the best that Marvel Studios can't make this movie. The hugely successful Avengers franchise has consistently succeeded at the box office, but it's possible that a solo Hulk movie could be the studio's first major misfire. Marvel not even having the option of making a Hulk movie might be the best thing that's happened to the studio since getting Spider-Man back.

15 THE DIFFICULT BRUCE/HULK BALANCE

Mark Ruffalo as Bruce Banner

Unlike almost every other superhero, Hulk and Bruce Banner are two different characters. When Steve Rogers puts on his Captain America uniform, he's still Steve Rogers. It's easier for fans to connect with the character because he's always present. Same thing with Iron Man, Black Widow, Dr Strange and just about every other Avenger. The character doesn't suddenly change into a completely different person when they assume their heroic persona.

The problem with Hulk is that when he shows up, Bruce Banner disappears. A solo Hulk movie would basically have two different main characters who can technically never be on screen at the same time (aside from any weird dream sequences). That's why Hulk works great in team up films, because the audience doesn't expect Banner or Hulk to be in every scene anyway.

14 HIS BEST FIGHTS ARE VS OTHER HEROES

Hulk and Thor Avengers

When Mark Ruffalo made his debut in Avengers (2012), director Joss Whedon purposely waited on showing him turning into the Hulk until he was alone with Black Widow, another of the film's heroes. When Banner Hulks out, the green goliath makes his onscreen debut attacking someone that audience doesn't want to see get beaten up. Whedon made this decision because he knew this would make the Hulk scarier and audiences would be more invested in the outcome of the fight.

The most memorable Hulk moments from the MCU have so far either been funny ones (like beating up Loki), or when he loses control and fights the other heroes. This is ultimately what makes Hulk interesting: he is a hero, sure, but there's always that chance that he'll lose control and start smashing the wrong people, like other heroes, who likely wouldn't be present in a solo film.

13 HE'S TOO INDESTRUCTIBLE

Hulkbuster vs Hulk fist shot

So far, Hulk's appearances in Avengers movies have included beating up both Thor and Loki, taking down a giant Chitauri flying monster with a single punch, manhandling Ultron and running straight into fortified Hydra bunkers (causing them to explode). During the finale of Avengers (2012), when Cap is coming up with a battle plan for the team, he points at the Chitauri forces and tell Hulk to smash. That's part of why audiences love the Hulk, because he's a rage beast that the Avengers just point at the bad guys.

The problem is that Hulk seemingly can't be hurt, which makes it seem like he's never really in danger. Sure, the Hulkbuster armor did well, but that was mostly because of either a sucker-punch, or because the Hulk finally started to snap out of Scarlet Witch's spell, basically beating himself. He's eventually going to out-punch whatever thing he's facing. Granted, this alone wouldn't be an insurmountable obstacle for a solo movie, but it is another problem to add to the pile.

12 PREQUEL-ITIS (KIND OF)

Thor Ragnarok Hulk

With Hulk set to appear as a guest star in Thor: Ragnarok (2017) and early set reports from Infinity War (2018) revealing his connection to another Marvel franchise, fans have a pretty good idea what the green goliath is going to be up to for the next few movies. That's actually a bit of a flaw, having characters appear across multiple franchises: guest appearances reveal where they're going to end up.

So, Marvel can always tell a story that fills in the blanks between all of these appearances, but that movie would end up suffering from the issue prequels often suffer from: a lack of true tension. Audiences will always know Hulk is going to be fine, because he's showing up in later movies (and unlike Captain America or Iron Man, it's not like someone else can just wear the costume).

11 HIS ALTERNATE PERSONALITIES

Hulk Age of Ultron red eyes

Part of the reason for the Hulk's popularity in the Marvel Cinematic Universe is that the studio really nailed the beast's personality. Unlike the other heroes, Hulk actually has several different personalities in the comics, ranging from a dumb, tantrum-throwing monster all the way to an intellectual scientist with a giant green body.

Hulk briefly became Joe Fixit, a gray-skinned Las Vegas enforcer in Incredible Hulk #347 (1988) by Peter David and Jeff Purves. There was also the tyrannical Maestro, who made his first appearance in Incredible Hulk: Future Imperfect #1 (1992) by Peter David and George Perez. Granted, Maestro is from the future and the heroic modern Hulk fought against him, but it still exemplifies an issue Marvel will face with a solo Hulk film. There's a lot of classic Hulk stories, but they unfortunately revolve around changing the character into someone audiences might not even recognize.

10 SAVING HULK APPEARANCES MAKES HIM SPECIAL

When the phase 2 lineup was announced and a Hulk movie wasn't present, one of the reasons given by the studio was that they wanted to save at least one character for the Avengers to make it feel special. While that might seem like a frustrating excuse to Hulk fans, it actually ends up being true.

Both Hulk and Iron Man are mainly making guest appearances in phase 3 as opposed to starring in their own films. The difference is that when Hulk showed up in the first Ragnarok (2017) trailer, the reaction was overwhelming positive; same with the second, incidentally. Tony Stark appeared in Spider-Man: Homecoming (2017) and Civil War (2016), but those appearances didn't build as much anticipation. Turns out, Hulk not having solo films of his own really does make his appearances feel more special.

9 HIS TIME MAY HAVE PASSED

Incredible Hulk vs Emil Blonksy

A reality that Marvel may need to face is that the time for a Hulk solo film may have passed by. Immediately after the release of Avengers (2012), there was a huge demand for more Hulk. Marvel's phase 2 slate, however, didn't have a slot for a solo Hulk outing, so he didn't appear again until Age of Ultron (2015). In between those movies, Marvel introduced new characters like Groot and Rocket, who were also well-received by audiences.

Even after that, characters like Spider-Man, Ant-Man and Black Panther have all appeared and been embraced by audiences. The fact is, Marvel makes great characters, and Hulk is only one of them. This isn't to say that audiences wouldn't like a Hulk film, it's just that they've been shown so many other great possibilities that they may have forgotten about Banner.

8 IS IT A COMEDY OR A TRAGEDY

Hulk smashes Loki

This entry isn't trying to say that comedy and tragedy can't be combined. In fact, the two often play well off each other. The problem that the Marvel Cinematic Universe's Hulk faces is that so far, his best received scenes have all been comedy (within the MCU). When Avengers: Age of Ultron (2015) tried to include some of the tragic elements of Hulk's story (by including a failed romance with Black Widow), those scenes were actually criticized.

Granted, those moments could've been better written, but it still demonstrates that Marvel's going to struggle to find the right balance. A Hulk movie shouldn't be a comedy, but that seems to be the only way Marvel's been able to successfully sell the character to audiences. They might have to spend more energy than it's worth to find the right balance.

7 IT'S DESTINED TO FAIL

Hulk vs Abomination

Marvel will never please all of their fans, especially when it comes to their movies. No matter how great a film is, there will always be some people complaining about how it deviated from the source material, while others will complain about all the silly references to comics. Normally, this wouldn't be a reason not to do a movie, but the Hulk is a special case.

The Incredible Hulk (2008) is still technically a part of the Marvel Cinematic Universe, but after Mark Ruffalo replaced Edward Norton in the role, many audience members don't fully embrace it. The movie still has plenty of fans, so Marvel has to choose between upsetting those fans by ignoring the plot threads set up in The Incredible Hulk, or they upset all the other fans by continuing storylines from a movie they've been trying to forget.

6 MARVEL NEEDS TO FOCUS ON SMALLER SCALE STORIES

Hulk and Black Widow Sakovia

When Thanos shows up on Earth with the Infinity Gauntlet in Infinity War (2018), it's a pretty safe bet that at least a few buildings will get knocked down. Throughout the three phases of Avengers movies, the stakes have been getting higher and higher. Four out of six of the Phase 2 movies end with an entire planet in danger, and even Guardians of the Galaxy: Vol 2 (2017) almost saw the Earth get destroyed.

While Infinity War has earned its big, blowout action scenes with a decade of build up, afterwards it'll be time to scale things down. Unfortunately for Hulk, that's not really what he's known for. Audiences might be worn out and sick of seeing entire cities get knocked over, and that's exactly what happens whenever Hulk gets slightly upset.

5 IT KEEPS MARVEL'S SCHEDULE OPEN FOR NEW PROPERTIES

Civil War team Iron Man

The biggest hurdle that Marvel Studios constantly has to overcome is staying fresh. The cinematic universe can't survive off the same three or four properties and the occasional team-up movie. New characters have to be introduced, either in their own movies or as cameos in other films, to keep the franchise feeling new.

Of course, Marvel has to balance the new characters with their popular, established franchises. Unfortunately, Hulk falls into the middle. As a film franchise, he's unproven, but a solo film won't come with the excitement of finally being able to see him on the big screen. Marvel already has a full plate with Guardians, Captain America, Ant-Man, Spider-Man, Black Panther and Captain Marvel, so finding slots open for new characters is already going to be difficult.

4 MARK RUFFALO'S CONTRACT IS RUNNING OUT

Hulk Avengers

Regardless of whether or not fans want a solo film (which, undoubtedly, many do), it's safe to say that almost everybody wants to keep seeing the Hulk show up in Avengers movies. He's a scene stealer for sure, and Bruce Banner has great chemistry with the rest of the team. Given the choice of either getting a solo Hulk film or giving the character another appearance with the Avengers, not a lot of people would go for the solo Hulk movie.

Ruffalo signed a six movie contract with Marvel. So, with Avengers (2012), Avengers: Age of Ultron (2015), Thor: Ragnarok (2017) and Avengers: Infinity War (2018), he's already at four. It's been confirmed that he'll appear in Avengers 4, leaving one film left on his contract. There's no guarantee that Ruffalo will agree for more movies, so Marvel needs to utilize him as best as possible while they have him.

3 SOLO MOVIES AREN'T ALWAYS THE BEST DECISION

Incredible Hulk

To be clear, this list is in no way meant to insult the Hulk as a character. Hulk should appear in tons of movies, it's just that a solo movie isn't necessarily the best option. This is a lesson Marvel learned the hard way with Thor. The Dark World (2013) isn't a bad movie, but it's often criticized because it felt so random and disconnected from the larger world set up in Avengers (2012).

Once these characters were all brought together, fans (not surprisingly) wanted to keep seeing them together. Ragnarok (2017), the sequel to The Dark World, is already receiving a warmer reception simply by adding the Hulk to the mix. Not every movie needs to be The Avengers, but team-ups are always fun to see and keep things feeling connected.

2 HULK ON THE RUN HAS BEEN DONE BEFORE

Hulk Avengers roaring

There have already been two Hulk solo films, and neither was all that well received. Hulk (2003) by Ang Lee received mixed reviews and resulted in the franchise being rebooted in 2008 with The Incredible Hulk, which was also met with mixed reviews. While the first movie was the only one that dealt directly with the Hulk's origin, both showed Banner on the run from the US military.

Even Avengers (2012) started off with Banner as a fugitive, and the ending of Age of Ultron (2015) returned him to that status. Fans have seen Hulk on the run before and been given plenty of opportunity to watch him smash tanks and take missiles to the chest. Since neither of those films were all that popular, there's no reason to try it again.

1 THE DIVERSITY ISSUE

Marvels The Avengers

Marvel's been called out for having a lack of diversity in their line-up before. While they do have plenty of diverse characters throughout their casts, the headliners of their movies have so far all been straight white men (there's even a joke about how most of them are named Chris). While Marvel's future definitely includes a more diverse line-up, they still have to deal with complaints on this topic.

Marvel has a huge roster of great characters. Nobody is complaining that a Black Panther or Captain Marvel movie is coming. Of course, a lot of people would be thrilled to see a solo Hulk movie, but Marvel would also have to acknowledge the fans that get upset. It might be better for them to focus on adding diversity for the time being.

Hulk will be stealing the show in "Thor: Ragnarok," which will hit theaters on November 3, 2017. But do YOU want to see him in his own flick? Let us know in the comments!