Out of hundreds of mutants in the Marvel universe, David Haller is among the most powerful. However, he doesn't receive that much attention outside of comic books, other than the odd appearance in animated shows such as "X-Men: Evolution" or "Marvel Anime: X-Men." That might change soon with the upcoming FX series, "Legion," starring Dan Stevens as the titular character.

RELATED: FX’s Legion Announces Release Date in New Trailer

Legion is a rich and incredibly complex character, which means he's difficult to really comprehend if you haven't been following the comics. Thus, it's understandable if you're one of those people who aren't quite familiar with him. Not to worry, though, that's what we're here! We've come up with 15 things you should know about the craziest X-man.

15 HE'S CHARLES XAVIER'S SON

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Charles Xavier met Gabrielle Haller at a psychiatric institution in Israel where he and Magneto were working to help survivors of the holocaust. Gabrielle was a patient there who began wooing Charles after he was able to break her free from a catatonic state. It's unclear when exactly, but the two had a child; unfortunately, Charles was unaware of him until David appeared much later. "New Mutants" #26 was David's first interaction with Charles and it was evident from the beginning that there wouldn't be a sudden stable father/son relationship between the two.

Throughout David's many appearances and his tragic madness, the one thing has remained consistent is David's abandonment issues, which has led to something of a tenuous relationship between him and his father. It didn't help that Xavier's focus was on all the mutants under his care, meaning he couldn't always be there for his son, though he did try. Worse still is that he has been forced to use David as a weapon in the past (as he did in "New Mutants" Vol.3 #14), which is never good for a blooming familial relationship.

14 HIS LIFE IS TRAUMA

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When you read about Legion's stories in the comics, you'll likely find that, for the most part, he's a good guy. But he's been through a lot. As was revealed in "New Mutants" #26 (written by Chris Claremont with artwork by Bill Sienkiewicz and Glynis Wein), David was the sole survivor of an anti-Israeli terrorist attack that killed his step-father. It was that event that fractured young David's already unstable mind and prompted the emergence of his mutant powers, which forced him to absorb the psyches of the terrorist leader, Jemail Karami, and the other terrorists who were all unintentionally incinerated by David.

It would not be the last time David's powers would traumatize him. Later, trying to do right by his father by ridding Xavier of Magneto, David travelled back in time to assassinate the future leader of the Brotherhood. Unfortunately, David's psionic knives hit Xavier, who dived into their path to save his friend. That kind of experience doesn't just disappear and would only make things more difficult for David's recovery as he searched for control over his personalities and powers.

13 HIS RELATIONSHIP WITH MOIRA MACTAGGERT

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After the initial traumatic attack, David was sent to Muir Island, the world's largest mutant research facility in the world, situated off the coast of Scotland. There, he was cared for by the facility's founder, Moira Mactaggert, who had been told about David's link to Xavier before inviting Charles himself over to help treat the young mutant. It had to be done after David unintentionally absorbed the psyches of two of Moira's assistants. We know that she had a lasting impression on David because one of his personalities took the form of Moira, a personality that attempted to express care for David's wellbeing.

If there's one person who can come close to understanding the kind of internal struggle and torment that David went through, it's Moira. The television series seems to have cut her character from Legion's life (with good reason, but we'll talk about that later), so it would be interesting to see who, if anyone, would fill the caregiver role in Legion's crowded head.

12 HIS DISSOCIATIVE IDENTITY DISORDER

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One of the reasons why Legion is such a complex character is the affliction he struggles with. He suffers from Multiple Personality Disorder (though in "Uncanny X-Men" #25, he was said to have been schizophrenic, a common mistake). In real life, this disorder is characterized by an individual exhibiting one or two alternating personalities, along with memory impairment. In Legion's case, there are over a thousand different personalities, each one controlling a different power. For example, the Jemail Karami personality was in control of David's telekinetic abilities and was, as with all David's personalities, fighting for absolute control.

David is affected by these on a daily basis and, as of yet, only one real David has appeared in "New Mutants" #20, a personality that the mutant Magik called "God-Mutant." In that form, he's capable of shifting time and warping reality and wiping out gods, as he did when he annihilated the Elder Gods in "New Mutants" #21. And that's just a taste of how powerful David is. He is constantly battling his inner demons, but was given a neural switchboard developed by Dr. Nemesis and Reed Richards in "X-Men: Legacy" #248, to help him gain more control.

11 HE KILLED HALF AN ISLAND

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Knowing David's full potential and the fact that he absorbs psyches makes stories like the "Muir Island Saga" (written by Chris Claremont, Fabian Nicieza and Peter David) that much more thrilling. For those who don't know, the Shadow King possessed Legion to become all-powerful using the mutants on Muir Island -- Polaris in particular -- as a nexus between the physical world and the astral plane. As Legion, Shadow King destroys a large part of the island ("Uncanny X-Men" #280) and kills the psychic mutant and friend of Mystique, Destiny.

This becomes a pivotal point in Legion's life, since it was her words in his head that caused him to try and keep his father's dream of peaceful mutant and human co-existence alive. It was also how Destiny came to survive the death of her physical body until she was able to return using alien technology.

10 HIS POWERS

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Aside from the ability to pull off that giant hairdo, David Haller possesses more superpowers than any other mutant. As we said before, with every personality comes a different power and David has more than a thousand. There's Cyndi, who possesses pyrokinetic abilities and Clown, who can blast energy beams from his mouth. Then there are others, who are werewolves, can spit acid and manipulate gravity.

David was at one point able to draw many of these personalities together as shown in "X-Men: Legacy" #21 with his squid-haired form, in order to fight a powerful yet hostile personality on the mental plane. It was something that his girlfriend, Blindfold, disapproved of, because it would mean death for her or David. It's difficult to imagine how the creators of the upcoming TV series plan on showing his thousands of personalities If at all), but it's something we would look forward to seeing. All we really can assume is that Dan Stevens has one hell of a performance ahead of him.

9 HE CAUSED THE AGE OF APOCALYPSE

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The 1995-1996 "Age of Apocalypse" storyline was a crossover event wherein the mutant Apocalypse conquers North America and begins wiping out humanity. It was an event that the X-Men had prevented, but this time -- without the existence of Charles Xavier -- it began 10 years too early. How did this happen? Legion, misinterpreting the deceased Destiny's words in his head, travels back in time to eliminate Magneto in the hopes that his death would allow Xavier's dream of mutant and human co-existence to properly grow.

Unfortunately, David accidentally ends up killing Xavier, which prompts Apocalypse to launch an attack a decade early. Luckily, Bishop was sent back in time from the Age of Apocalypse to prevent Legion from making this fatal mistake. This just goes to show you what terrible things can occur if Legion or any of his personalities is left unchecked. It's also a great example of who David is as a person. We can see that he's not necessarily evil, but he's not exactly a wholly good person either. We can also see how desperately he wishes to build some kind of relationship with his father, which is something a lot of people can relate to... though without the catastrophic mutant powers, presumably.

8 HE'S NIGH-IMMORTAL

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With all his power, you can rest assured that David will probably never meet any true end. When Bishop killed him to prevent the Age of Apocalypse, the only remnant of him that seemed to remain were a few fragmented personalities manifesting as spirits. Legion himself suddenly appeared, back from the dead in "New Mutants" Vol.3 #1. We later find out that Magik was the one that revived him for one purpose: to wipe the Elder Gods from existence. Still, considering that one of his personalities has the ability to make duplicates of himself, Legion may not have even needed Magik to return, so long as one of those spirits remained.

In fact, after recently wiping himself from existence, we might just find Legion doing that exact thing to return. After all, in "X-Men: Legacy" #24, it is revealed that some part of him remains in Blindfold's mind. That doesn't mean you should stop worrying about him, though. As you'll see, though, David can always return one way or another; the threat lies with David's stolen personalities dominating or destroying his own. Speaking of which...

7 HIS BEST STORIES ARE IN HIS HEAD

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Another reason why Legion is such a unique character is because most of his more thrilling tales don't take place in the physical world. Even his love life takes place in his head... no, not like that. From his struggle against the terrorist Jemail Karami to the resolution he found with his father, his greatest battles were seldom seen, heard or felt by others; and yet, it often impacts the outside world in monumental ways.

As was said before, he's constantly battling his other personalities for control and that means that sometimes, he loses; if only momentarily. That's why it's so exciting to read his battles, like the one that took place in "X-Men: Legacy" #21, against the personality named Fiend, who took on the form of Xavier. Though David was able to hold his own through a collective named Gestalt, Fiend was still able to make a staff sergeant in a Russian submarine launch a missile. While we know that that was all the work of his enemy, the rest of the Marvel Universe -- with the exception of Blindfold -- would see it as just random violence and anger, making him a truly tragic hero.

6 BLINDFOLD

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With so much instability, David needs an anchor to help him against the tide, and it seems he found it in Ruth Aldine, the mutant known as Blindfold. Born without eyes (or eye sockets), Ruth found herself an outcast, even at the Xavier Institute. But that wasn't the worst thing she'd been through. She too suffered a fragmented mind, thanks to her abusive and murderous brother, who stole a fraction of her power and left her mind broken. Clearly, Legion and Blindfold had a lot in common, and were better equipped to understand one another. That is perhaps why they were able to aid each other in such impressive ways.

Blindfold, who usually stutters, finds that when in Legion's mind, she's free of that impediment. Legion, meanwhile, has grown much more confident because of her, allowing him to better control his personalities (which is obviously good for everyone). If you needed proof of Legion's good heart, look to Blindfold, who has become his moral guide, fighting for Legion to become the man she knows him to be when they're together in the mental plane.

5 HE WIPED HIMSELF FROM EXISTENCE

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Because of Blindfold, Xavier's death and all the destruction he'd wrought after losing control of his powers in "X-Men: Legacy" Vol.2 #1, he had a lot to come to terms with, and in many ways he did. Blindfold was able to pass on a message from his father, which placed Legion on a path to peaceful resolution. A lot of people didn't agree with this ending for Legion, but "X-Men: Legacy" writer Simon Spurrier has stated that it is something he intended from the series' earliest stages.

Spurrier wrote, "The central goal was to bring David to a place where he’d overcome everything he reasonably could: his enemies, his own inability to trust others, his pride, his confusion regarding his father, and most importantly, his own mental illness." That works well with the message Blindfold delivered to David, his father letting him know that he was proud of his son. That's what he needed to become his whole self again, embracing all his power and deciding for himself how best to use it. In the end, he decided not to play god and removed himself (almost) from the equation, which, even if you don't agree with it, is noble.

4 HE'S AN X-MAN (SORT OF)

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Teams like Excalibur have fought his rampaging personalities and the X-Men have fought Legion possessed by Shadow King, after the Jack Wayne personality shot Storm down. In "X-Men: Legacy" Vol.2 #2, his personalities took turns carving out a path of destruction around the world. Despite all that, they would have all been lost without him. He saved the X-Men from the Nimrods in "New Mutants" Vol.3 #14, though Xavier was initially unsure of allowing him to fight . Then, of course, there was his timely arrival when the X-Men battled the forces of the Elder Gods.

Despite all the good he's done, he's an understandably difficult mutant to trust --  a liability, if you will -- which is why he's not exactly the most active member of the team, even if he was under their care at the Xavier Institute. He's been an adversary just as often as he's been an asset and saved lives as easily as he's taken them. X-Men learn how to control their powers and use them for the greater good, something Legion has immense trouble doing. He's unable to be a functioning member of the X-Men, which may give the writers of the upcoming series a lot more freedom with the character.

3 THE SHOW TAKES PLACE IN THE X-MEN UNIVERSE

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With FX releasing "Legion," it makes sense that people would expect the television series to connect with the films somehow, in a similar way to Marvel's "Daredevil" or "Agents of S.H.I.E.L.D," which are affected by the events of the film and vice versa. Initially, FX President John Landgraf had stated that the series would be set in a parallel universe of sorts, meaning Legion would essentially exist in a world of his own. This has since changed, with Bryan Singer stating that the series had been written to fit in with the "X-Men" film universe.

That doesn't mean you should expect to see familiar characters from the films returning, although showrunner Noah Hawley has stated that Charles Xavier would probably appear somewhere in the series. The show must of course stand on its own first. It'd be a shame if a character as great and versatile as Legion was to be out-shined too often by fan favourites.

2 NOAH HAWLEY IS LEGION'S SHOWRUNNER

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If the name Noah Hawley sounds familiar, it might be because he was the creator of the fantastic FX series, "Fargo," winning a Prime-Time Emmy Award for Outstanding Mini-Series. If you're a fan of Legion and are still worried about this live-action adaptation, you'll be glad to know that Hawley was a fan of the X-Men growing up. You can expect that he'll respect the character without binding him to the stories, or even the limitations of his comic book counterpart.

That being said, Hawley still seeks to surprise fans of the character and showcase his affliction with the respect and unpredictability it deserves, taking inspiration from shows like "Mr. Robot," where the audience can never really know for certain if the things they're seeing on screen are true. This makes the character of David that much more unpredictable and interesting, since he probably won't be too sure of reality either.

1 LEGION: TV VS. COMIC

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Legion in live-action and in comic books.

We definitely cannot expect the David Haller in the series to completely reflect the character in the comics. For example, we know that Katie Aselton has been cast as David's older sister, Amy, a character who didn't exist in the comics. She's described as being positive about her brother's affliction and relatively "normal." That raises an interesting question -- would the emotional support result in a vastly different Legion? Keep in mind that the comic book character didn't have many people to support him. His own father was unfortunately distant and the only real emotional support he had was Blindfold, whereas in the series, he has his older sister and a new love interest, Syd Barrett.

Of course, you'd have to expect a milder Legion on TV. The series has him in an psychiatric facility; not quite as well equipped as Muir Island, but good enough to give us, as an audience, a chance to explore the character. Given the setting, however, we can probably expect the level of destruction to be dialled down quite a bit. That being said, we're still very much interested in seeing the character of Legion explored in-depth, perhaps even in ways the comics couldn't.

What do you love most about Legion? What are you looking forward to in his TV series? Let us know in the comments!