On one wall of the actor Michael Emerson’s Manhattan apartment hangs a large self portrait he drew about 40 years ago. In the intentionally distorted image, Emerson peers out menacingly from behind his circular glasses. His wife, the actor Carrie Preston, thinks it serves as a fitting summation of his career.

“You know, Carrie brought this up recently saying, ‘There’s the template for so much of what you have done as an actor,’” he said. “For me it was just a laugh. It’s still the same mix of having fun and yet being a little, what’s the word, terrifying.”

It’s true: If you want someone to be creepy on television, you call Michael Emerson. The 69-year-old actor had his breakout role in 2000 playing a serial killer in “The Practice,” a performance so memorably distressing it won him a guest actor Emmy. He went on to unsettle viewers for years as the unpredictable Ben Linus in “Lost,” and as the computer wizard Harold Finch on “Person of Interest.” This year he showed up for one episode of the Prime Video series “Fallout,” from the “Person of Interest” creator Jonathan Nolan, as a quietly menacing scientist. They aren’t all bad guys, but you’re never quite sure.

Emerson is currently inhabiting his most ghoulish role yet, in the aptly named Paramount+ show “Evil,” returning for its fourth and final season on May 23. Emerson plays Leland Townsend, a demonic emissary who constantly torments the heroes, a group of investigators played by Mike Colter, Katja Herbers and Aasif Mandvi. This trio works for the Roman Catholic Church to determine whether various strange goings-on are the result of satanic forces or more mundane phenomena. Leland’s main goal is to promote the forces of darkness by any means possible.

In Emerson’s hands, Leland is a captivating, often frightening agent of chaos who is surprisingly goofy for someone who is OK with child murder. In the new season, he is raising his biological son — he nefariously arranged the baby’s conception earlier in the series — and believes the child is the Antichrist.

“I don’t know anyone that does unsettling better than Michael Emerson,” Michelle King, who created “Evil” with her husband, Robert, said in a video interview.

It’s a skill he can evidently turn on. On a sunny afternoon in April, he invited a reporter into his home and was happy to discuss his décor, which includes a series of vintage-style “Lost” posters and Preston’s collection of “energy rocks.” A small, elderly dog named Chumley was curled up on the couch after a bit of early suspicion regarding the intruder.

“I don’t think I’ve ever worked with an actor who was more different than the character they were playing than Leland and Michael,” King said. “It’s hard to imagine where he’s pulling that from, because he is so very different from that in life.”

Christine Lahti, one of Emerson’s “Evil” co-stars, concurred. “He’s the opposite of Leland,” she said, describing him as “gentlemanly, kind, sensitive.”

Emerson said he has been drawn to “grotesquerie” since he first started acting, in school plays in Iowa where he grew up. “I was always the bespectacled little guy with the shrill voice who would play the old man or the clown or the wizard,” he said. He would do drawings of “ghoulish figures that have no eyeballs.”

There’s still a taste of the macabre in his otherwise very pleasant penthouse: There’s a large drawing, by Emerson, of a cat skull he found under a house he was working on in St. Augustine, Fla. Florida was one of the detours Emerson took during his lengthy journey to a thriving acting career.

“When young actors ask me ‘What advice do you have?’ I say, ‘Can you answer this question: Could I wait 20 or 30 years to be a success as an actor?’” he said. “Because that’s what it took me.”

He moved to New York to act after college but found it hard to break into the business, and eventually pivoted to magazine illustration after taking weekend classes at Parsons while doing retail jobs. His first marriage, which ended in divorce, brought him to Jacksonville, Fla., where he did regional theater. A graduate acting program took him to the Alabama Shakespeare Festival, which is where he met Preston when she came to town to play Ophelia in a production of “Hamlet.” Emerson was Guildenstern.

Preston now stars in the CBS procedural “Elsbeth,” also created by the Kings. It’s a family business, although the cheery sleuth Elsbeth could not be more different from the disconcerting Leland. (Emerson marvels at Preston’s work on “Elsbeth”: “Where does she come up with that? It’s just so great.”)

Emerson credits his Shakespearean training — twice he played Iago, the chatty schemer of “Othello” — for his ability to keep viewers on edge. “Iago forces the audience to collaborate with him and makes them complicit in his mischief,” he said.

When Emerson reads a script for “Evil,” he starts to imagine how unpredictable he can be. “Is the line maybe secretly funnier than anyone imagined? Let’s try that,” he said. “Or playing a counter strategy: Being gleeful about a thing that the audience expects you to be glum about. Or be upset about something that no one else in the world would be upset about.”

Herbers, who plays the forensic psychologist Kristen Bouchard on “Evil,” said acting opposite Emerson is like a game of “high-level chess.” He delivers a line about, say, murdering her character’s children as if he were offering “a bouquet of flowers.”

“We meet in the scene, and we surprise each other, and I think we excite each other,” she said.

Emerson said the “Evil” crew is thrilled when there is a Leland scene to shoot. (Herbers confirmed this.) “They rather delight in Leland,” Emerson said. “They just know it’s going to be scenes that are just dangerous and have a little crackle and also sly humor and many comical upsets or frustrations.”

Over the course of the four seasons, Leland has confessed his troubles to a devil therapist, posed as a video game character to threaten Kristen’s daughters and danced in a wheat field in a particularly hilarious dream sequence. He’s been drenched in blood and pelted with Antichrist vomit. In one scene, Leland sings the song “Kids” from “Bye Bye Birdie.” Emerson sometimes feels as if the Kings are testing him: “Can we make it so dopey that Emerson won’t do it? But I’ve defeated them.”

Michelle King said Emerson is “willing to do anything, no matter how crazy it is.”

“That’s been completely freeing,” she added. “He understands how to make the rhythms odd, and that makes the character odd.”

So would Emerson want to play someone kindhearted for a change? Not necessarily. He doesn’t have a bucket list of roles, but has considered one challenge he’d like to tackle.

“I play such talkers that I’ve often thought I’ll be interested someday if somebody offers me a role that is kind of silent, or nonverbal, or mute somehow,” he said.

His voice grew quieter as he finished that sentence. It was, yes, somewhat unsettling.