Superhero movies are more popular than ever and, as a result, so are rumors about superhero movies. The moment a studio announces a new project, the internet is immediately awash in speculations, suggestions, scuttlebutt and suppositions galore. Will this character appear? Will that storyline be adapted? And most importantly, who is going to play who? Bringing beloved comic book characters to life is serious business, especially as far as the longtime fans are concerned. So it's not surprising that fans and news outlets alike devote so much time to discussing the subject.

It is equally unsurprising that many casting rumors turn out to be false. Movies take a long time to get made, which leaves plenty of time for bored and/or anxious observers to spread theories they either love or virulently hate, regardless of the credibility of the evidence -- assuming there is any evidence at all -- behind any given bit of gossip. Trying to sort the wheat from the chaff can be difficult, especially when the rumors are as seemingly grounded as the ones featured on this list. Join us as we remember 20 casting rumors that seemed reasonable at the time but later proved to be as empty as a promise from Loki!

20 EMILY BLUNT AS CAPTAIN MARVEL

Emily Blunt in A Quiet Place

Captain Marvel is Marvel's first film to star a female superhero on her own instead of as part of a group. Understandably, such an important role is bound to draw a ton of attention from fans, many of whom have been waiting for years for a female-led superhero flick. Before Brie Larson was cast, one option that fans found particularly compelling was Emily Blunt.

Blunt was, of course, asked about the rumors. She responded by saying that she hadn't even been asked to join the Captain Marvel cast. But fans' eagerness to see her in a superheroic role isn't surprising, as this wasn't the first time the rumor mill attached Blunt's name to a Marvel character. Previous theories had cast her as the Black Widow and Agent Peggy Carter. Well, if Ms. Blunt is actually interested in joining the MCU, there's plenty more superheroines where they came from...

19 JAKE GYLLENHAAL AS BATMAN

Jake Gyllenhaal in Demolition

Poor Jake Gyllenhaal. He's been an also-ran for the role of the Dark Knight since the early '00s. As Christopher Nolan prepared for Batman Begins, Gyllenhaal was one of the top choices to play Batman, until he lost the part to Christian Bale. After Bale walked away from the franchise, Jake Gyllenhaal's name naturally floated to the top of the list of potential replacements. Again Warner Brothers passed on Gyllenhaal, this time in favor of Ben Affleck.

But now that Affleck is rumored to be leaving the cape and cowl behind, the internet is wondering if Jake Gyllenhaal will get to star in the upcoming Matt Reeves film The Batman. Will Gyllenhaal be a runner-up yet again? Or will he finally get his shot at playing the Caped Crusader?

18 ROBIN WILLIAMS AS VARIOUS BAT-VILLAINS

Robin Williams in Dead Poets Society

Almost from the moment the Burton/Schumacher series of Batman films began, there was speculation about legendary comedian Robin Williams joining the fun. First, the rumors claimed that he might play the Joker in 1989's Batman.  That role ultimately went to Jack Nicholson, who earned a Golden Globe nomination for his performance. Williams' name then came up in connection with Batman Forever as a contender for the role of the Riddler. But in the end, Jim Carrey donned the Riddler's green tights.

A third and final rumor suggested that Williams might get to play Hugo Strange, a mad scientist who has bedeviled Batman since 1940. Sadly, this rumor proved as insubstantial as the first two, and the world was deprived of the chance to see Robin Williams go toe-to-toe with the Dark Knight.

17 ALLISON WILLIAMS AS THE INVISIBLE WOMAN

Allison Williams in Get Out

The most contentious casting news regarding 2015's Fant4stic was, unfortunately, the selection of Michael B. Jordan as the Human Torch.  A small but vocal segment of fans objected to a black Johnny Storm. Their complaints all but drowned out other casting rumors, including once suggesting that the studio was considering Allison Williams, star of the TV show Girls, for a role.

Many assumed this meant Williams would play the Invisible Woman -- a reasonable conclusion, given that Sue Storm is the only female character of note in the film. Once the dust settled, House of Cards star Kate Mara ended up filling Sue Storm's invisible shoes. Williams instead went on to costar in the groundbreaking film Get Out. Given the muddled mess Fant4stic became, we're going to go out on a limb and say she dodged a bullet.

16 RASHIDA JONES AS JANET VAN DYNE

Rashida Jones in Parks and Rec

For a while, speculation suggested that Parks & Recreation's Rashida Jones would costar in 2015's Ant-Man as Janet van Dyne. In the comics, Jan is the winsome Wasp and a founding member of the Avengers. So, naturally, many fans were excited at the possibility of finally getting to see the Wasp on the big screen.

This rumor turned out to be false on two levels. First, the character Jones was allegedly up for turned out to be not Janet van Dyne but Hope van Dyne, Janet's daughter. The character of Janet van Dyne hardly even appears in Ant-Man. For the brief time she does show up, she is played by Hayley Lovitt. Second, Jones was ultimately not cast in the film at all. The role of Hope van Dyne went to Evangeline Lilly.

15 JOHN CENA AS SHAZAM

John Cena

A wrestling fan's dream come true! Wrestling legend John Cena was in the running to play Captain Marvel, aka Shazam, the superheroic adult alter ego of young Billy Batson. The fact that Dwayne "The Rock" Johnson, another popular former wrestler, has long been slated to play the villainous Black Adam only made this rumor even more exciting.

But alas, this is one wrestling showdown that will have to wait for another time. Zachary Levi, who previously played the swashbuckling Fandral in the Thor movies, has been cast as Shazam rather than Cena. As for Black Adam, both he and Johnson have been dropped from the film all together. But before you get too sad about the lack of wrestlers in Shazam, remember that there is still a Black Adam film in the works.

14 KATEE SACKHOFF AS CAPTAIN MARVEL

Katie Sackhoff in The Flash

In the summer of 2014, Battlestar Galactica alum Katee Sackhoff got fans talking with the suggestion that she might be up for a part in Avengers: Age of Ultron. More specifically, Sackhoff teased that she would be playing Captain Marvel, a character who even today has yet to appear in the Marvel Cinematic Universe. Could this be true, fans wondered? Would Sackhoff be the one to finally bring Carol Danvers to life?

Well, obviously we wouldn't be talking about it on this list if the answer had been yes. Sackhoff did not appear in Age of Ultron, and neither did Captain Marvel. Sackhoff did, however, finally make it into a superhero universe. Just last year, she nabbed the role of the villain Amunet in season four of The Flash.

13 MATTHEW MCCONAUGHEY AS CAPTAIN AMERICA

Matthew McConaughey in How to Lose a Guy

It's hard to remember now, but a mere ten years ago, the Marvel Cinematic Universe was barely a thing yet. Iron Man had only just hit theaters, and Marvel was still searching for their Captain America. Who could possibly fit the bill as the Sentinel of Liberty? What about the guy from How to Lose a Guy in 10 Days? Yes, at one point, fans looked at Matthew McConaughey as a real possibility to star in Captain America: The First Avenger.

In the end, of course, Marvel went with Chris Evans. Evans' casting wasn't without controversy, as many fans didn't think they'd be able to see him as anything but the Human Torch. But now, fans are mostly agreed that McConaughey, while a talented actor in his own right, could not have handled the role nearly as well as Evans has.

12 JAMES McAVOY AS PROFESSOR X (IN NEW MUTANTS)

James McAvoy as Professor X

Professor Charles Xavier is such an integral part of the X-Men's origins that it's hard to imagine a team of mutant superheroes coming together without him. This logic is probably what led to the speculation that James McAvoy, who plays Professor X in the most recent X-Men movie franchise, would film a cameo for the movie New Mutants.

New Mutants focuses on five mutants -- shocking, we know -- who are trapped in and then escape from a secret facility. Surely they will need Professor X's assistance to learn how to use their powers and adjust to a normal life after their imprisonment? Apparently not. Neither McAvoy nor Xavier will appear in the film at all. Looks like the New Mutants will have to find someone else to lead them.

11 JAKE GYLLENHAAL AS RICK FLAG

Jake Gyllenhaal in Nightcrawler

Boy, comic book fans really do want to see Jake Gyllenahaal in a superhero movie, don't they? In addition to the never-ending Bat-rumors, Gyllenhaal's name briefly appeared as a contender for such high-profile Marvel roles as Spider-Man and Doctor Strange. He was even more briefly thought to be up for the part of Colonel Rick Flag in 2016's Suicide Squad. Flag is the team leader, which is a fancy way of saying he's the poor idiot tasked with keeping the Squad members in line.

But like we said, this rumor's shelf life was quite short.  he job of wrangling Harley Quinn and company went to RoboCop actor Joel Kinnaman. As for Gyllenhaal, he has yet to land any superhero-related role at all. But with as many super-roles as he's been considered for, he's got to nab one sooner or later.

10 JESSICA CHASTAIN AS LILANDRA

We know that Jessica Chastain has scored a role in the upcoming film X-Men: Dark Phoenix. But beyond that? Your guess is as good as ours. Her character's name is still a secret. And where there are secrets, there are bound to be rumors. The most convincing of these rumors posited that Chastain might be playing Lilandra, leader of the Shi’ar Empire and one-time love interest for Professor Xavier. Lilandra played an integral role in the original "Dark Phoenix" storyline, so surely that solves this particular mystery?

Not so fast. Chastain has made it quite clear that she was not cast as Lilandra. In fact, we have since learned that Chastain's character is much more villainous than Lilandra, though the actual identity of her role remains a topic of fan speculation.

9 RYAN GOSLING AS GREEN LANTERN

Ryan Gosling in La La Land

Back before fans realized what they were in for, Green Lantern was a highly anticipated film. And of course, the question on everyone's minds was: who would take on the mantle of the Green Lantern? Rumors ran rampant for quite some time. For a while there, Canadian actor Ryan Gosling was one potential contender for the green CG tights. His handsome, Hal Jordan-esque looks and Oscar-nominated acting skills convinced more than a few fans that Gosling could easily make a success of the role.

But eventually Gosling’s name faded from the running, replaced by other famous names that also went nowhere. Warner Brothers finally settled on some other Ryan from Canada, and Green Lantern hit theaters in 2011. The less said about all that, the better.

8 BRYAN CRANSTON AS LEX LUTHOR

Bryan Cranston as Walter White

Bryan Cranston spent five years playing Walter White, a bald, morally complicated character that audiences couldn't help loving. Lex Luthor, also a bald, morally complicated character, has spent virtually his entire existence trying to destroy Superman, much to the delight of superhero fans everywhere. Both are wildly popular, so fans went nuts at the suggestion that Cranston might appear as Luthor in Batman v. Superman: Dawn of Justice.

This rumor gained so much steam that one fan even put together a trailer of what Dawn of Justice might look like with Bryan Cranston in it. Sadly, all of the excitement came to an end when Jesse Eisenberg was cast. But we all know how much DC likes telling and retelling Superman's story on film. So perhaps someday...

7 CHLOE GRACE MORETZ AS THE PINK RANGER

Chloe Moretz as Hit Girl

Chloe Grace Moretz has already had some experience with playing teenage superheroes. In 2010 and 2013, she brought the vigilante Hit-Girl to life in the Kick-Ass movies. So it seemed perfectly plausible when Moretz's name came up as a potential candidate for the role of Kimberly, aka the Pink Ranger, in the 2017 Power Rangers film.

But then someone thought to actually ask Moretz about the rumors. Her response? She said that, aside from the fan speculation, she hadn't heard anything about her being in Power Rangers, as the Pink Ranger or anyone else. As it turned out, the studio had their own ideas about who should play the Pink Ranger. Those ideas led to the casting of Naomi Scott rather than Chloe Grace Moretz.

6 TYRESE GIBSON AS GREEN LANTERN

Tyrese Gibson in Fast and Furious

So far, the only Green Lantern to appear on the big screen is Hal Jordan. But fans have long dreamed of seeing one of the other Lanterns -- especially John Stewart -- get their day in the spotlight. For a brief period in 2015, fans were convinced Stewart's time had finally come, and that Tyrese Gibson had grabbed the role. After all, audiences already love Gibson for speeding around in fast cars in The Fast and the Furious franchise. Who wouldn't want to see him speeding around with a fancy alien power ring?

Fueled by a convincing piece of fanart, the rumors eventually made their way to Gibson himself. Unfortunately, Gibson shot the rumors down kindly but firmly. He thought he would make a good Green Lantern, but no one had actually offered him the role.

5 LEONARDO DiCAPRIO AS THE JOKER

Leonardo DiCaprio in The Revenant

In September 2017, a tantalizing new rumor hit the superhero fandom. Allegedly, superstar Leonardo DiCaprio was interested in replacing Suicide Squad's Jared Leto as the Joker. Not only that, but DiCaprio would be doing so in a Joker origin movie produced by Hollywood legend Martin Scorsese. Overnight, the internet lit up with concept art of DiCaprio in white face paint. Some folks excitedly suggested that DiCaprio could earn himself another Oscar if he went ahead with the role.

But as of this writing, this rumor is pretty definitely dead. The chatter about DiCaprio has been replaced by chatter about Joaquin Phoenix. And unlike DiCaprio, Phoenix has actually made comments indicating he's receptive to the idea of playing Batman's most notorious nemesis. So will we actually get to see Phoenix in the role, or is this just another cruel joke?

4 DAN AMBOYER AS GREEN LANTERN

Dan Amboyer in Batman v Superman

Dan Amboyer is most famous for his roles in TV shows like The Blacklist and Younger. But for one brief shining moment in 2016, fans had cause to believe that Amboyer might be the new Green Lantern. The rumors started when Amboyer got the role of "drone pilot" in Batman v. Superman: Dawn of Justice. This led to speculation that Amboyer's character was really Hal Jordan, a pilot who goes on to become the Green Lantern. Could Warner Brothers be planning to surprise audiences by introducing Green Lantern to the DCEU?

Well, if Warner Brothers does have any plans for the Emerald Crusader, they don't involve Dawn of Justice or Dan Amboyer. The film came and went with nary a Lantern in sight, and Amboyer did indeed play just a drone pilot.

3 GRANT GUSTIN AS THE FLASH

Grant Gustin as the Flash

Since 2014, Grant Gustin has won the hearts of fans as the title character of TV's The Flash. So why, fans figured, shouldn't he be given the opportunity to bring his magic to the big screen? As soon as DC announced that the Flash would appear in 2017's Justice LeagueFlash fans started dreaming about their TV hero becoming their movie hero as well.

But those dreams will have to remain dreams. Ezra Miller is now firmly established as the DCEU's version of the Fastest Man Alive. Miller is even going to star in a Flash solo film, which is scheduled for release in 2020. Still, it's hard to feel too bad for Gustin, considering how many fans he has and how much they obviously love him.

2 NEIL PATRICK HARRIS AS THE MUSIC MEISTER

Film Neil Patrick Harris as Doctor Horrible

"Mayhem of the Music Meister!" is a special musical episode of the cartoon series Batman: The Brave and the Bold. Fan-favorite actor Neil Patrick Harris guest-starred as a singing supervillain named the Music Meister. The episode, and Harris’ role in it, proved very popular with viewers. Years later, in 2017, it was announced that The Flash and Supergirl would be having a musical crossover featuring none other than the Music Meister as its main villain.

Many fans hoped that Neil Patrick Harris would be invited back to play the live-action version of the role he originated in animated form. Those fans ended up disappointed. While the Music Meister did play an important part in the crossover, Broadway alum Darren Criss had the honor of bringing him to life.

1 JON HAMM AS SUPERMAN

Jon Hamm as Don Draper in Mad Men

Superman is without doubt the most iconic superhero in the world. Therefore, selecting the right actor to play him is very important. For a while, some people thought that Jon Hamm was that actor. Looks-wise, he certainly fits the bill. With his strong jaw and clean-cut look, all you have to do is slap a pair of thick awkward glasses on him and you're good to go.

Personality-wise, Hamm had a bit of an upstream swim to convince audiences that he could play the upstanding Man of Steel. His most famous role is the endlessly shady and manipulative Don Draper on Mad Men -- the exact opposite of Superman's relentlessly honest image. But it didn't matter in the end. Henry Cavill landed the role of Superman in 2011. Was this a good decision or a bad decision? We’ll leave it up to you to judge.