Dan Stevens on everything you need to know about 'Legion'

"Legion" officially premieres tonight based off the Marvel Comics about a young man David Haller diagnosed as schizophrenic. It turns out that not only is David's diagnosis wrong, he's a mutant with incredible powers.

There's a lot of buzz about this gritty FX show, but more questions than anything else.

Dan Stevens, who plays Haller in the series, stopped by "Popcorn with Peter Travers" and explained everything to know before checking out the eight-part season 1. Stevens is well-known from hits like "Downton Abbey" and the upcoming "Beauty and the Beast," and now he's poised to take on the mantle of Marvel superhero.

Here are some key takeaways about "Legion":

It's Shot From a Different Perspective

"He's a guy who's been told he's a paranoid schizophrenic his entire life and is certainly exhibiting a lot of these symptoms. There's lots of strange things happening to him," Stevens said. "He's diagnosed as one thing, institutionalized pretty much his whole adult life, then a group of people come in and tell him something radically different."

Though the mutant world will be wild and fun like in the comics, viewers are almost invited "inside his head," Stevens said about the audience experience.

The X-Men are Present, But Don't Expect To See Them Much

"You don't need to," the actor said. "You can know that it takes place in [that] universe or not. That's not really material to what we're getting at."

Now, calm down, Stevens said there will be "little hints and tie-ins," like the fact that Haller is the "lost son of Professor X." But it's not the center of the show.

It's Also a Love Story

On top of this main character finding out he's the son of one of the greatest mutants of all-time, he's in love.

"That's a madness that we all can experience at some time," he said. "How does that feel? This guy in love, how does she react to him and all his different manifestations?"

The woman he's in love with, Syd Barrett played by Rachel Keller, also can't be touched, which adds some layers to the mess. (Sounds like Rogue in X-Men.)

"It's a great obstruction," Stevens joked. "You guys are madly, passionately in love, but you can never touch, or certainly in the beginning of the story."

Fans of the Show 'Fargo,' Might Like 'Legion'

Noah Hawley, the creator of this new project, also wrote much of the acclaimed "Fargo" series, which is also on FX.

"He wants to play with the audience," Stevens said about Hawley's new show, which he calls "insane."

"He can be a real tease with the information he gives you," he added, "which can drive you crazy."

In fact, it's hard to tell the time frame of the show. Some elements look like they are from the 70's or 80's, but others have a modern touch.

"There are visual touchstones ... it plays with our nostalgia," Stevens said. "It has a certain feel like, 'I know where this is,' then something will come in and someone [has] this iPad type thing and you're thrown."

Check back with ABC News in a few weeks to get the full interview and find out all about Stevens' role in "Beauty and the Beast."

Disclaimer: Marvel and ABC News are both part of parent company Disney Co.