It’s hard to see yourself as a leading man when you’ve built a career as an oddball underdog. Just ask Jimmi Simpson, the 43-year-old actor who’s played a series of characters that highlight his strange sensibility while sometimes masking his considerable acting chops.

There was, of course, his absurdist role as Lyle the Intern on Late Show with David Letterman; the hard-to-handle antagonist Liam McPoyle in It’s Always Sunny in Philadelphia; and the creepy guinea-pig-petting hacktivist on House of Cards. But a few years ago, his career started to diverge from lurker-in-the-corner territory. Jonah Nolan and Lisa Joy hired him as the Man in Black in Westworld flashbacks, and then Charlie Brooker cast him as Walton in the Season 4 opener of Black Mirror, the much acclaimed “U.S.S. Callister.” This new phase in Simpson’s career rolls right along next month when he stars opposite Sir Ben Kingsley and Jacki Weaver in Epix’s Perpetual Grace, LTD, the latest from Patriot show-runners Steve Conrad and Bruce Terris.

“A lot of the characters I play are [there] to spike the punch of the story,” said Simpson during a recent interview at one of his favorite haunts in Los Feliz. “You have this story and everyone’s brilliant, and then you need something kind of interesting to happen. That’s a lot of the parts that I get. In Perpetual Grace, I’m part of the punch. I’m part of the nutritional value. That Steve Conrad trusted me to be the straight man of this really kind of revolutionary show means the world.”

The casting was something of a risk for Simpson, he told me. For the first time in Simpson’s eclectic 19-year career, he had found himself being courted for the lead role on three different television shows. He turned them all down in the hopes that something more “artful” would come along.

“No one’s ever cornered me in that way,” he said. “But I feel like the specificity of my career that I’ve gotten unwittingly, because of taking what you can get when you’re a funny-looking character actor, has led me to have a very specific résumé that I’m very proud of. It’s kind of singular in my eyes. I like that it’s a little different, a little weird, and there’s not too much mainstream [stuff] for mainstream sake on it.”

So he waited, promising his agents that if nothing panned out in six months, he’d “play a janitor on the Disney Channel.” Then, Conrad’s script about a firefighter named James who abandons his crew—and then abandons his identity, only to become entangled with two dangerous hucksters (Kingsley and Weaver)—landed in his lap.

“The voice was so clear, and the story was so thrilling in a way that I’ve never seen a television story,” he said. “It reminded me of falling into my favorite novels, where you’re literally in another world and you can feel everything. I saw it, and I said, “Yes.’”

For Conrad, the casting of Simpson was a no-brainer. “Every time I saw Jimmi in something—Lyle the Intern, Liam McPoyle—I knew he prepared it,” said Conrad. “And I could feel the confidence that that creates, the instances when a tremendously talented person works very hard. That’s when they have a command on it. Jimmi has a command on it.”

Simpson’s perpetually under-the-radar status is a product of his years growing up in New Jersey, where no one he knew had a career in the arts.