FX’s “Legion” hasn’t so much played its cards close to its chest as it has thrown a whole bunch of cards at the viewer in a perception-altering round of fifty-two pickup, defying us to figure out what game is even being played. Six episodes into its eight-part first season, the new X-Men-adjacent series finally offered some answers. Which is about time, since so far it’s been forcing us to question absolutely everything. Most exciting among its revelations for comic fans was when (SPOILERS!) The Demon With The Yellow Eyes -- the frightening apparition that has been haunting possibly-schizophrenic mutant David Haller since childhood -- was revealed to be the Shadow King.

RELATED: Legion: 15 Things You Need To Know

Rather than being a manifestation of David’s multiple personalities or fractured mental state, the Shadow King appears to in fact be responsible for the troubled telepath’s psyche. But who is he? A recurring villain from the “X-Men” comics, the parasitic force is one of the strongest links to the show’s source material. Here are 15 things you should know about the Shadow King.

15 HE'S NOT A MUTANT

Despite having a history with the X-Men which covers several decades (in print terms; in-universe, it’s been even longer!), the Shadow King is not actually a mutant. His origins have been kept purposefully vague, or at least, conflicting accounts of where he comes from have been presented. That is similar to the way myths in real life evolve over time, or how multiple theories are posited for uncanny phenomena. It’s also par for the course with the countless retcons and reboots that befall your average comic book character.

One constant through all of those explanations is that the Shadow King himself is definitely not a mutant. In fact, he lacks a physical form entirely. To survive in the physical world, he routinely occupies the bodies of others. A lot of the time, he has chosen mutants as hosts, since those with psychic abilities can provide a handy boost to his own. So technically, whilst his emissaries on Earth are often mutants, the creature known as the Shadow King himself -- who, it’s assumed, is some sort of body-less malevolent consciousness -- is not.

14 HE MIGHT PREDATE HUMANITY

The Shadow King and The Brood

While his origin story has never been set down with any sort of certainty (referring to him as a “he” is barely even assured), comic readers have been given a few clues as to the Shadow King’s parentage over the years. It has been posited that, lacking a physical form, he may simply be a force that exists across the multiverse. In fact, his birth is said to have followed the first nightmare, seizing on that surge of negative psychic energy in the collective unconscious... not to get all Psychology 101 on you for a moment.

Apocalypse is often cited as the First Mutant, but Shadow King might even predate En Sabah Nur, and outdo him in terms of psychic ability. Since the dawn of humanity, he has been leaping from one host to the next, feeding on the dark parts of people’s souls and boosting his own powers by taking over the body of the Egyptian mutant Amahl Farouk, who he was in control of from the beginning of the 20th century and long into that perilous part of human history which wasn’t exactly short on darkness on which he could feast.

13 HE CAN CONTROL MINDS

He’s not got a lot to offer in terms of strength, what with him lacking a physical form and all, but the Shadow King’s psychic ability is second to none. Well, technically it’s second only to Charles Xavier, but more on that in a moment. In order to transcend the astral plane and have his presence felt in the physical world, he has to have a strong arsenal of telepathic and telekinetic abilities, which have only gotten stronger thanks to his possession of a series of powerfully telepathic mutants.

Thanks to this power, and the absence of a body, the Shadow King also has very few weaknesses. In the psionic world, only rival psychics can hope to hold a candle to him, or else the magic users of the Marvel Universe who are equipped to deal with such matters. He’s relatively limited in his abilities in the physical world, and he can use his psychic powers to take over a person’s body, but he’s then limited to the strength and superpowers of those hosting him. That’s not to say he’s easy prey when he possesses a non-mutant body...

12 MANIPULATION IS HIS GAME

Magneto vs the Shadow King

Not only does the Shadow King’s mind (does he technically even have a brain?) boast those incredibly powerful psychic abilities, but the guy -- or rather, the metaphysical being -- is smart. Deviously so. Like a fox, even, if he even cares what those are. It would be hard for him not to pick up a few skills in manipulation, having existed since the dawn of humanity and relying on harvesting the darkness in other people for his survival.

A supervillain is nothing if he hasn’t got a good brain working behind all the bells and whistles. Audiences have already seen how his insidious influence works in “Legion,” where the Shadow King has squatted in David Haller’s mind and twisted his memories, feelings and perceptions of the very world around him for his own gain. In the comics, he has planned and enacted countless schemes where he has managed to exploit good guys with his Machiavellian ways, sometimes without even having to use his mind control capabilities.

11 HE HELPED FORM THE X-MEN (KINDA)

Professor Xavier and the Shadow King meet via astral projection

He’s technically been around for eons, but the first time readers clapped eyes on the Shadow King (in his guise as Farouk) was in 1979’s “Uncanny X-Men” #117, by John Byrne and Chris Claremont. A flashback story set in the “Thieves Quarter” of Cairo, it was partially about Charles Xavier’s encounter with a young Storm, who picks his pocket, and Amahl Farouk, the crime lord who ran the Egyptian city’s underworld. After retrieving his wallet from Kid Ororo, he was struck by a psychic attack, which he traced to a nearby tavern.

It was there that he met Farouk, who he quickly identified as one of the most powerful psychics he had yet met in his travels. Farouk claimed his attack was a warning, hoping Xavier would flee after telling him of an even more powerful telepath in the area. That, obviously, was a lie, since said powerful telepath was living inside Farouk’s body. After an unsuccessful attempt to recruit him to Farouk’s criminal enterprise and duking it out on the astral plane, the young Charles realized not all mutants used their powers for good. It’s at that moment he resolved to form the X-Men.

10 HE'S HATED XAVIER FOR YEARS

The Shadow King in the guise of Amahl Farouk

So, technically, the Shadow King instigated the foundation of the X-Men. There’s a certain poetic justice to the fact that Xavier’s mutant team has since been the one to thwart all of his evil schemes. Having tasted a little of Professor X’s psychic powers, however, Farouk couldn’t stay away. Game recognize game, after all. Being a parasitic being without physical form, inhabiting the body of Xavier would allow him to amplify his existing telepathic abilities to world-conquering levels.

That initial meeting also hurt Farouk/the Shadow King’s pride, and he’s been trying to get revenge ever since. In once instance, following the “House of M” crossover, he escaped from his prison on the astral plane and took host in a Xavier of an alternate reality. When he hasn’t been able to get to Xavier, he’s managed to get at his loved ones, including his estranged son David Heller, as seen on both the comics page and in “Legion."

9 THERE'S A REASON HE'S SO LARGE

The Devil With The Yellow Eyes in Legion

The various iterations of the Shadow King seen in “Legion” have run the gamut of peculiar to genuinely nightmarish. Aubrey Plaza’s Lenny is a menacing, androgynous oddball, but the truly memorable scenes with the villain have included the round-headed Angry Boy taken from a twisted children’s picture book and -- even worse -- the literally-named Demon With The Yellow Eyes: a grotesquely obese creature who shambles forward with glowing pupils and a zombie-like intensity.

The weight of the Demon (played by first-timer Quinton Boisclair, and apparently inspired by reality series “My 600-lb Life”) is in keeping with comic book depictions of the Shadow King. Historically, hosts the bad guy remains in for an extended period wind up getting pretty large. The Shadow King is ravenous for souls to consume, so too are his physical bodies greedy for grub, gobbling up excessive amounts of food with a gluttonous glee comparable to the Shadow King’s own disturbing metaphysical appetite.

8 HE WAS A NAZI

Amahl Farouk as the Shadow King in Excalibur

As one of the ultimate evils in the universe, who feeds on human suffering in as literal a sense as you can feed on an abstract concept, and one which has existed since time immemorial, it stands to reason that the Shadow King hooked up with the Nazis at one point. In his guise as Amahl Farouk, he teamed up with Wolfgang von Strucker and Geist, the “Captain America” villains and special agents to Hitler. Farouk was enlisted in a plan to depose King Edward and install a fascistic leader of Britain who would spread the fuhrer’s toxic ideals further afield.

The Shadow King’s end of the bargain involved conducting a magic ritual to aid the plan, sacrificing soldier Alasdhair Kinross in a demonic ceremony which would topple the British monarchy. What actually happened is he brought the modern-day Kitty Pryde and Rachel Summers back in time. The demons got angry, possessed Farouk and brought out the Shadow King, who killed the Nazi soldiers present and had von Strucker accusing him of treason before fleeing. Not the worst fate, being bad-mouthed by a Nazi.

7 HE FIRST APPEARED IN NEW MUTANTS

Sam Guthrie and Karma in the New Mutants by Bill Sienkiewicz

Having already had experience with other mutants, and long since burying his association with the far-right, the Shadow King remained in, well, the shadows for a good few decades. Biding his time, waiting for the next opportunity to seize control over a more powerful host than the aging and sagging Amahl Farouk. He saw that opportunity in the pages of “New Mutants,” the Claremont and Bill Sienkiewicz series about a younger team of recruits to the Xavier School, and the young psionic mutant Karma.

In one of the most surprising twists this side of “The Judas Contract,” it was revealed in “New Mutants” #34 that the Shadow King had been controlling Karma’s mind ever since issue six. For two years the character readers had been enjoying had in fact been in the thrall of one of the most powerful villains in the X-Men franchise. Augmenting his own abilities with Karma’s telepathic powers, the Shadow King rebuilt his criminal empire in the lawless country of Mardipoor.

6 HE HAUNTS STORM

Storm is possessed by the Shadow King

The ongoing conflict between the Shadow King and Charles Xavier is a battle for the latter’s formidable psychic abilities. The former’s constant battles with X-Men veteran Storm? That’s personal. They first met on the streets of Cairo where, pre-mutant powers, a young Ororo Munroe picked the pocket of Charles Xavier. After her abilities manifested and she was recruited as a member of the X-Men, Storm returned to her former Egyptian home to help the New Mutants fight the Shadow King, then occupying the body of Karma.

During a time when she had been reverted to her younger form, more vulnerable and less in control of her powers, he tried to take over her mind (before moving onto poor young Legion.) After another thorough beating and return to the astral plane, he reemerged as leader of a tribe that worshipped Storm, goading her into facing him again by killing one of her relatives. Unlike the ongoing Xavier spat, the Shadow King’s antagonism towards Storm seems more about straight vengeance than an attempt to gain her power.

5 HE ENSLAVED AN ISLAND

Shadow King possesses David Haller during the Muir Island Saga

Eventually, that particular spell was broken thanks to the intervention of Magik, who once again did battle with the Shadow King on the astral plane to dismiss his insidious influence. He lay dormant for a period again, licking his wounds before taking possession of the body of a dead FBI agent. From there he tried to kidnap a Storm who had been reverted to childhood, before catching sight of an even more enticing prospect: David Haller, better known as Legion, who went looking for the missing Storm using the telepathy-boosting Cerebro headset.

What he found was the Shadow King. Pouncing on the opportunity to inhabit another super-powerful psychic, the villain effectively took full control of Muir Island, the home base for X-Men ally Moira MacTaggert, whilst retaining his puppeteering of Farouk as well. With multiple powerful agents, he came the closest he has to achieving his goal, and could only be stopped by severing his connection to the physical plane. Mystique shot Farouk, effectively ending the Shadow King’s control, but also facilitating the mental collapse of David in the process.

4 HE INSTIGATED A PSYCHIC WAR

Charles Xavier and the Shadow King duel in the Psi-War

Readers saw neither hide nor hair of the Shadow King for a long while after the Muir Island storyline, owing to his imprisonment on the psionic plane by Xavier. Unfortunately, following the events of the Onslaught crossover event, the X-Men’s phenomenally powerful leader found himself without his psychic abilities. Seizing this opportunity, the Shadow King broke free of his astral prison and set about regaining his power by posing as Ananasi, the leader of an African tribe.

Before too long his true identity was uncovered, leading to a confrontation with Psylocke (who he dismissed as a second-rate Jean Grey,) riling her up into accidentally damaging the collective subconscious of every being on Earth by hitting a member of the tribe with a psychic blast. Humans across the world experienced nosebleeds and deja vu; psychic mutants and other superheroes were seriously injured, with Doctor Strange, Emma Frost, Jean Grey and Spider-Man all affected. Psylocke eventually returned him to his confinement on the disrupted psychic plane.

3 HE'S FOUGHT OTHER MARVEL HEROES

Storm rescues the Black Panther from the Shadow King

For the most part, the Shadow King has been an adversary of the X-Men, but he’s also crossed paths with the wider Marvel Universe on more than one occasion. There’s the aforementioned “Psi-War,” where his manipulation of Psylocke resulted in a psychic shockwave that affected heroes, mutant and otherwise. At one point he met the V-Battalion, a secret organization made up of Golden Age superheroes (and, later, their descendants), whose support he was promised if he could provide information about the evil force known as the Everlasting.

As for A-listers, the Shadow King’s ongoing conflict with Storm eventually lead him into direct opposition with her one-time husband: T’Challa, the King of Wakanda better known by his superhero identity Black Panther! Having escaped once more from the astral plane, he emerged in Wakanda, where he killed a local priest and framed a new X-Men recruit called Gentle for the murder. When the Panther showed up, he took control of the hero’s body, intending to force Storm to chose between her husband and the X-Men, thwarted only when he tried to possess his arch nemesis and was confronted with the panther god, Bast (naturally).

2 THE ASTRAL PLANE IS HIS DOMINION

Psylocke vs the Shadow King in X-Treme X-Men

The astral plane has been a common location in Marvel Comics, for psychics and mystical heroes alike. It made its small screen debut in the fourth episode of Legion, when David Heller was introduced to Oliver Bird (played by Jemaine Clement of New Zealand musical comedy duo “Flight of the Conchords”), another telepath who had called the plane his home for nearly two decades. Why? Well, it’s got a lot going for it, compared to the physical world. Those powerful enough can shape the plane to their will, even if their will just involves jazz records.

The Shadow King’s usage of the astral plane goes a little bigger than that in its scope. It’s an ethereal world for an ethereal being, who has called it home since the dawn of time. Where most of the Marvel characters capable of projecting their minds into the plane otherwise have physical bodies back in the physical world, the Shadow King does not. That means he’s got a leg up on those who face him: he’s spent eons gaining power, fostering a human hatred which literally fuels him, and is consequently a force to be reckoned with in this eerie place.

1 HE'S BEEN ON SCREEN BEFORE

The Shadow King in Wolverine and the X-Men

The Devil With The Yellow Eyes, The World's Angriest Boy in the World, Lenny Busker. The Shadow King has worn a lot of faces in “Legion,” and they’re among his most memorable screen appearances. But they’re not the only ones. Previously, the manipulative mind reader has been an antagonistic presence in the “X-Men Legends” video game, as well as “Wolverine and the X-Men” and the ‘90s “X-Men” animated series.

Drawing mostly on writer Chris Claremont’s “X-Men” comics as it did, the Shadow King’s presence in the ‘90s series seemed assured. Played by voice acting veteran Maurice Dean Wint, he appeared in a flashback to Xavier’s time in Cairo, hewing closely to the comic story but for making Farouk trim and bearded rather than bald and fat. In “Wolverine and the X-Men,” voiced by Kevin Michael Richardson, he duels both with a young Storm in flashback and faces Emma Frost on the present-day astral plane.

What do you know about the Shadow King? Tell us what's on your mind in the comments!