What Is The Astral Plane On 'Legion'? The Marvel Cinematic Universe Has Already Introduced The Concept

Michelle Faye/FX

FX's Legion has introduced viewers to plenty of mind-bending concepts over the course of its first three episodes — body-swapping, memory mapping, the Devil With The Yellow Eyes — but things are about to get even trippier in the weeks ahead. What is the astral plane on Legion? And how exactly is it going to come into play in future episodes? Well, in some ways it already has, although viewers may not have known what to call it.

In last week's "Chapter 3," David and Syd briefly traveled to the room where his sister Amy was being interrogated by Division 3. They appeared as only flickering, transparent versions of themselves, and were only capable of being seen by the villain known as The Eye. Then they disappeared and re-manifested back into the pond at Summerland. Fans of the Marvel comics on which showrunner Noah Hawley's TV series is based will know that they just witnessed astral projection — one of David's many abilities. In fact, the concept of the "astral plane" plays into both David's story and the Marvel comics mythos in many significant ways.

So what is it? The astral plane is a separate dimension that exists parallel to our own, where our souls go when they leave our bodies. Although it's a new concept to Legion, it's not a new concept to Marvel fans. If you saw Doctor Strange this past November, then you were introduced to it right alongside that film's protagonist, Stephen Strange. The Ancient One briefly pushed Stephen's soul out of his body into the Astral Dimension in their first encounter; he later returned to it when he was on death's door, brawling with a villain in the emergency room; and he visited it one final time when The Ancient One was dying, and watched her astral form disappear just as her physical body died.

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(Note: the astral plane is separate from the other, different dimensions that Doctor Strange visited throughout the film such as the Mirror Dimension where he brawled with Kaecilius and the Dark Dimension where Dormammu resides.)

Other than David's and Syd's astral projection, last week's episode also introduced the concept of the astral plane in one other, subtler way. During the hour, viewers were introduced to a brand new character who is sure to be integral to the future of the show, although we never even saw his face… or any of his physical form, for that matter. We learned that the voice that can be heard throughout the halls of Summerland — including the complicated, storytelling coffee machine — belongs to none other than Melanie's husband, Oliver Bird.

According to Melanie, Oliver built Summerland several decades ago, but has been absent for the past 20 years. It was left ambiguous whether her husband had died or gone missing or what; but in an interview with Syfy Wire, actress Jean Smart teased that her absent spouse has spent the intervening years trapped on another level of existence. "[Melanie] gets more fun for me when my husband's character gets introduced, as she hasn't seen him in decades," she revealed. "He's been on an astral plane, which is a hard rendezvous. What an extraordinary thing to play, not seeing your husband for 20 years."

Frank Ockenfels/FX

Given that we know Flight Of The Conchords' Jemaine Clement has been cast as Oliver Bird (both his voice and his body) it's clear that his introduction — and the question of whatever it is he's been doing in the astral plane for all those years — will be an integral piece of Legion's puzzle moving forward.

While the introduction of the astral plane will likely raise a lot of questions among viewers — especially those less familiar with the Marvel source material — it does seemingly provide an answer to of the show's most pressing mysteries: the identity of the ominous villain, the Devil With The Yellow Eyes. There have been many fan theories about who this terrifying creature really is, but now it appears almost certain that he's an adaptation of a comic book character called the Shadow King.

In the comics, the Shadow King is a manifestation of the dark side of consciousness, who came into existence when the first human had the first nightmare. Ever since, he has flitted around the edges of human history, occasionally entering our dimension to wreak havoc and do battle with the X-Men — and when he's not facing off against Professor X and his team of mutants, the villain makes his home in the astral plane.

It makes sense that, out of all the options, Legion's Devil would turn out to be the Shadow King, since that character has a history with David Haller in the comics: he once possessed the powerful mutant, controlling his prodigious powers in order to do battle with Professor X during the "Muir Island Saga" storyline. Although the show has yet to introduce Charles Xavier (we've only glimpsed David's father in shadowy memories), a version of this plot could still make its way to the small screen, with the astral villain possessing David's mind in order to gain a corporeal existence… and take over our world.

So while the astral plane is an exciting concept for Legion to be exploring, it's also clear that it's an incredibly dangerous place for David to go. He better be careful in his psychic wanderings — or he could find himself stuck there just like Melanie's long lost husband.