With FX's "Legion" about to formally introduce the Shadow King as the big villain of Season One, we thought it might be helpful to explain just who the character is, and what role he has played in the history of Marvel Comics' X-Men.
We first met the Shadow King in 1979's "X-Men" #117 (by Chris Claremont, John Byrne and Terry Austin), or at least we were led to believe the person we met was the Shadow King. In an important flashback issue, while he believed his X-Men to be dead, Charles Xavier recalled the time years earlier when he met Amahl Farouk in Cairo. This was the first mutant Xavier had ever met who used his/her powers for evil.
A popular trope in comic books, particularly in Marvel's X-Men titles, is telepathic battles that take place in the mental plane, or rather the "astral plane." The one between Xavier and Farouk was among the first times this trope was used in an "X-Men" comic book.
In the end, despite Farouk being much more experienced with the use of his powers in this way, Xavier was able to defeat him, and Farouk died (in a brilliant piece of sequential storytelling by Byrne and Austin) ...
The idea that there might be evil mutants out there changed Xavier's outlook on his life dramatically. This ultimately led to him forming the X-Men, as he believed there needed to be both an outlet out there for good mutants to receive training (or, as we learned later on with how he handled Rogue, even a place for "bad" mutants to come so that they could get help, as well, which, in turn, would keep them away from the bad groups of mutants) and to train good mutants to fight against the bad mutants.
However, while Xavier believed Farouk to be dead, it was then revealed his psychic consciousness remained in the astral plane, just without a body. He was then able to make contact with Karma of the New Mutants (Xavier's then-latest generation of students) and secretly control her for many months, slowly turning her evil (and fat). This was finally revealed in "New Mutants" #34 (by Chris Claremont and Steve Leialoha), where Farouk became obsessed with Storm of the X-Men, who he captured along with the New Mutants ...
Karma was able to ultimately fight off his control and he went back into the astral plane.
He showed up a few years later during a period when the X-Men had disbanded and their members were spread around the globe. Storm had been de-aged and was on the run without her memories. Seeing her in such a weak position made Farouk possess FBI Agent Jacob Reisz and hunt down Storm, as she was "the one who got away." He even began to use his powers to turn innocent people into "hounds" that would serve him. It was at this point that he began to be referred to as the Shadow King. Storm was saved by Gambit.
However, while they escaped, the Shadow King began to consolidate his power base on Muir Isle. He discovered that a change in Lorna Dane's powers (after being possessed by the villainous Malice for longer than Malice had ever possessed anyone before) had turned her into a sort of emotional amplifier. He could then use her to control a whole island worth of people at once. This became the Muir Island Saga, as Xavier and the free X-Men teamed up to free their friends from the Shadow King's control.
After Reisz's body was destroyed, the Shadow King took over the body of Xavier's own son, Legion ...
Xavier was able to defeat the Shadow King and banish him to the astral plane, but Legion's mind was seemingly destroyed in the process, and Xavier's body was crippled once more.
It was at this point that it became clear Farouk was never actually the Shadow King, but rather it was the other way around: The Shadow King has long lived on the astral plane as a being of malevolent psychic energy. He has just used hosts over the years, and he tends to use the same host as much as he can. He used Farouk for decades before he met Xavier. He also seemed to plan on sticking with Reisz as long as he could, as well.
After Xavier's own mind was corrupted by merging his with Magneto during "Fatal Attractions," which led to the creation of Onslaught, the Shadow King was able to escape from the astral plane. This led to his next major storyline, "Psi-War," where he began to affect all psychics on Earth!
In the end, in "X-Men" #78 (by Joe Kelly, German Garcia and Art Thibert), Psylocke sacrificed her own telepathic powers to trap the Shadow King within her mind ...
That worked for a few years, but then Psylocke was killed soon after the X-Treme X-Men team was formed, and the Shadow King was freed and set upon the world once more.
Since then, the Shadow King has become a recurring nuisance, especially in the works of Chris Claremont. The Shadow King fought the X-Treme X-Men following Psylocke's death, he then went to another Earth and conquered that Earth's X-Men and had them fight against New Excalibur and most recently, he fought against Nightcrawler, turning the rest of the X-Men against him. All of those adventures were penned by Claremont.
However, the Shadow King also showed up in a few other places, including perhaps most notable in a Storm/Black Panther miniseries where he tried to turn Wakanda against their new Queen (all part of his obsession with Storm). He also met up with Psylocke again when she was part of Uncanny X-Force.
Due to this unique powers, the Shadow King is not really a villain that you're ever going to get rid of period, but due to his ability to take over and corrupt people, he makes for a fun, recurring villain. His connection to Legion in the comics makes him a perfect fit for the "Legion" TV series. It also keeps the door open for a future appearance by Charles Xavier.
"Legion" airs Wednesdays at 10 p.m. ET/PT on FX.