Early on in the first season of HBO’s sci-fi-Western hybrid Westworld, William, the wide-eyed, wary guest of the android theme park, was established as one of the show’s pivotal characters. By questioning everything about a mind-bending world in which people pay to indulge their darkest impulses, the character, played by Jimmi Simpson, became our proxy. But don’t assume that means Simpson will spill the beans on what to expect when the show returns this spring: He pleads near-total ignorance about the plot, only allowing that it’ll be epic. “Everything I hear, I’m like, ‘Oh my God.’”

But first he stars on February’s Unsolved on USA Network, based on the murders of Tupac Shakur and the Notorious B.I.G. Simpson plays Russell Poole, an LAPD detective who went to his grave believing that police corruption played a role in the killings. (An unrelated film inspired by the same story, starring Johnny Depp as Poole, will be released later this year.) Simpson found the role among his most challenging. Despite being “used to making people laugh, creeping them out, intimidating them,” as he describes it, he was caught off guard playing Poole, whose singular focus on the case bordered on obsession. “I left every day of work feeling like a piece of shit—I was sure this would be the big failure of mine.” Now, he says, “it’s some of my proudest work.”

Which is saying something for the forty-two-year-old actor: Simpson’s résumé goes back nearly twenty years and includes dozens of credits. His most memorable work to date came in the wake of two life-altering experiences in 2012. The first was his divorce (from New Zealand actress Melanie Lynskey). The second was a motorcycle accident (a hit-and-run that left him convulsing on an L.A. freeway). Before then, he says, “I had found this rhythm of getting parts, and I was grateful for them, but I kind of let it define me. Like, I’ll be the goofball who says something crass, and then I can totally pay my rent. I lost my ability to see it”—acting—“as having value. And then my life turned around.” Ever since, he’s tried to take roles “where I’m wrestling with humanity.” And with the occasional non-humans, too: He stars in the Star Trek–inspired episode of the latest season of Black Mirror, which creator Charlie Brooker told him is one of his all-time favorites.

Later in the year, Simpson will costar alongside Andrew Garfield in Under the Silver Lake, helmed by It Follows director David Robert Mitchell. As his good fortune continues, Simpson, who grew up in northern New Jersey and cut his teeth in theater, remains humble. “I conduct myself as if I am a spaceman in Hollywood,” he says. “I don’t want to do anything fancy. I don’t want people to send me free clothes. I just want to be grateful for this craft they let me do.”

Related: