NEW YORK — Erin Wilhelmi, who plays one of the two most egregious major characters in Broadway’s “To Kill a Mockingbird,” could not believe the words out of the stranger’s mouth. The actress was stationed at a door of the Shubert Theatre, seeking donations at the end of a designated charity performance, when a departing patron plunked some money in her plastic bucket.

“She said, ‘Here you go, you little slut’ as she was walking by!” Wilhelmi recalls. “And I was like: I’m not going to do this anymore!”

It can be fraught and isolating, it seems, portraying a white character activating the racial overtones of a beloved novel brought to the stage. Just ask Fred Weller, essayer of Bob Ewell, the patently evil father of Wilhelmi’s Mayella, who forces her to concoct the story that sends a blameless black man, Tom Robinson, to prison for rape.

“When people from my building or my kids’ schools see it, it can be weird sometimes,” he says. “I had this one parent, she didn’t know what to say to me. She didn’t say ‘Good work’ or anything — and I helped her get the tickets, too!”

For the legions of people who’ve read the novel — and the legions now flocking to Aaron Sorkin’s moving stage adaptation — Bob and Mayella Ewell are, of course, the villains of the story, albeit driven by disparate levels of animus and fear. Which is why I sought out the actors who bring them to life eight times a week. I wanted to know what the experience was like for them, if their own worlds are changed by having to inhabit such reprehensible human impulses at a time when some of the worst characteristics of our national heritage seem to be reinfecting the nation’s discourse.

It was the words of actor Gbenga Akinnagbe, who plays the falsely accused Tom, that heightened my curiosity. In this newspaper’s op-ed pages in May, Akinnagbe wrote of his anguish: “What I did not anticipate was how deeply it would affect me, how wearing it would be, to play a part that makes me the daily object of racist invective and racial violence for a majority-white audience.”

Weller and Wilhelmi’s characters are the sources of much of that invective: The n-word spews from their characters regularly — a requirement that both actors say still unsettles them, after more than 225 performances. That is nothing, of course, compared with how the word falls on a black person’s ears. The two actors agree that, from the beginning, it’s been the acceptance they’ve felt from black actors in the cast that grants them permission to play these fictional figures truthfully.

“From the earliest days of rehearsal, the African American cast members have been the most supportive,” Weller says, sitting beside Wilhelmi at a table at Sardi’s, the historic Broadway dining spot across West 44th Street from the Shubert. The speaking of racist language is so troubling, both actors report, that even using the epithet in the ongoing rehearsals, when new cast members are brought in, feels like a violation. “It was weird saying the n-word out loud, with no audience,” Weller says. “It was because we weren’t performing for someone. We weren’t ‘wearing’ our characters.”

“And you know,” Wilhelmi adds, “a dialect coach said to me that she could detect a blip of a pause after I would say the n-word, and she explained: ‘You have to go straight through it — because it’s going to show that you’re uncomfortable with it. Just use it, because in the ’30s, that’s what they did.’ ”

“To Kill a Mockingbird,” set in Alabama in the Jim Crow era, takes as its heartbreaking premise novelist Harper Lee’s conviction that a black man facing trumped-up charges was nevertheless doomed. The Bob and Mayella of the novel, conjured via the narration of Atticus Finch’s daughter, Scout, played onstage by Tony winner Celia Keenan-Bolger, are shadowy, malevolent figures. To make them more fully theatrical, Sorkin sought to sharpen Bob as a foil for the tale’s lawyer-hero, Atticus, played by Jeff Daniels.

“I wanted to make Bob Ewell smart. Able to make a coherent argument in support of his hatred,” Sorkin says in an email. “And because I don’t really recognize the subtle nuances between the alt-right, white nationalists, white supremacists, white separatists and skinheads, I put Ewell in the [Ku Klux] Klan. But the bass note running under everything is the same thing driving the hate today: ‘You think you’re better than me.’ ”

Mayella, at 19 a woman battered and raped by a monstrous father, at least gets the grim consolation of pity. “Mayella’s been a victim of poverty, ignorance and her father and I wanted that to be clear,” Sorkin says. “We can never forgive Mayella for the choice she makes, but we should be able to understand it.”

Weller and Wilhelmi have been portraying Bob and Mayella since the play was in its workshop phase and Sorkin was figuring out who they were. “Fred and Erin are giving the performances of any playwright’s dreams,” Sorkin says. “Watching them in rehearsal just made me want to write more.” As the writer sought to raise the dramatic stakes, Bob became ever more despicable, until a cast member joked during a rehearsal: “Aaron, why don’t you just have a cat come on every night, and Fred can just kill it?”

The sense, though, of some unspeakable, incestuous conspiracy between Bob and Mayella is affirmed in Sorkin’s conception: During the 2½ -hour production, directed by Bartlett Sher, the characters exchange no audible words, their only observable contact a whisper by Weller into Wilhelmi’s ear as Mayella takes the stand and Bob is banished from the room. What threat does he utter to ensure Mayella sticks to their damnable lie, that Tom attacked Mayella after she asked him to take an ax to a piece of furniture in her yard?

“What keeps her from cracking,” Wilhelmi says, “is the siblings”: the unseen younger children of widower Bob. “What would happen if she’s gone? She’s the oldest, and I do think the physical violence that she gets from him will just turn on them.”

Onstage, Weller — a New Orleans-born stage and film veteran last seen in Washington in director Ivo van Hove’s revival of “A View From the Bridge” at the Kennedy Center — looks cruelly menacing, a grizzled bundle of rage. Wilhelmi, a native of Louisville who played one of the false accusers in, coincidentally, van Hove’s “The Crucible” on Broadway, seems so enveloped in shame and mortification you expect Mayella to implode. Offstage, liberated from the darkness, they are gregarious and witty.

Weller has had to navigate the chasm between his own nature and the evil he embodies: With trepidation, he says, his wife brought their children, 11 and 9, to see “Mockingbird” a few weeks ago — “they were thoroughly prepped,” he adds — but only let them stay for the slightly less upsetting first act. (The verdict? “They loved it.”) Like any actor, he’s had to come to terms with his role and believe in his character from the inside out, no matter how brutal the character is. “Because I have to understand how he came to be what he is, and I have to come up with my own story. That’s not something that anybody would want to hear, or should hear.”

Some audience members understand the art of transformation. Some don’t. (Wilhelmi, by the way, is still collecting money at the door some nights for charities such as Broadway Cares/Equity Fights AIDS.) Her folks came, and, well, they reacted the way moms and dads tend to: “They are just happy parents that are like, ‘Yay! You’re working!’ ”

But both actors are keenly aware that what they have a part in igniting in “Mockingbird” is disturbing.

“The first week of curtain calls,” says Weller, “I wasn’t sure if I should bow or kind of do an apologetic shrug.”