Spittle flies. Ethan Hawke’s eyes are a cloudy blue, his teeth crooked, his beard prophetically long and more salt than pepper. He is shouting Old Testament scripture in a quavering whiskey growl and pop-quizzing his sons about Bible verses in the thick of a gunfight.

Hawke is John Brown, the violent anti-slavery crusader who collaborated with Harriet Tubman and Frederick Douglass, famously raided the federal armory at Harpers Ferry, Va., and stoked the Civil War. Playing America’s abolitionist vigilante in the Showtime limited series “The Good Lord Bird,” which premieres Sunday, is the role of a lifetime for him — a “giant, greasy, fat, rich turkey leg on Thanksgiving morning,” Hawke says. He co-created the show with James McBride, and co-wrote all seven episodes.

Hawke couldn’t stop laughing when he read McBride’s 2013 novel, which tells Brown’s story with some dramatic license and Coen brothers-style black humor, and felt called to evangelize it — not least because Americans know next to nothing about Brown.

“They might know the word ‘Harpers Ferry,’” Hawke says. “But: ‘Was that the Revolutionary War? Oh wait, he was an abolitionist, right? He was a lunatic, right?’ It’s interesting that society thinks a person that took up arms to stop 4 million people from being bought and sold and treated as horribly as African Americans, the criminal way in which they were treated — a person who tries to take up arms to stop that is not insane. It’s the society that’s insane.”

Brown is one of the most radical transformations in the actor’s career, which began 35 years ago. In July 1985, Hawke starred in “Explorers” as a bright-eyed teenager named Ben who travels into space and meets a family of aliens, an encounter he believes will change his life. After auditioning a bunch of “plastic,” trained actors, Joe Dante gave this 13-year-old from Texas his first screen role because “he was very endearing, he was very awkward,” Dante says. “He was tripping over the wires, and he was really cute.”

“Explorers” was the latest in a wave of sci-fi kids movies, and it opened on the same day as the Live Aid benefit concert. It tanked. Hawke went back to school and back to the real world, feeling like “the ship had left the station without me, that my dreams were never going to come true, because clearly I’d had the opportunity and I’d blown it.”

Hawke told Dante years later that he felt personally responsible for the film’s commercial failure “and that he carried this burden around with him all the time, of it being on his shoulders that the picture didn’t work,” Dante says. In reality, Dante was pressured to release an unfinished cut of the movie. “I disabused him of this notion,” he says. “I mean, I couldn’t have been happier with him.”

There’s something of Ben in many of Hawke’s characters through the years — even John Brown — in that he is a true believer who comes face to face with crushing disappointment. Think of his second major role, as the painfully shy Todd in “Dead Poets Society,” who comes out of his shell only to lose his roommate and his inspiring teacher. Or the rookie cop in “Training Day,” whose idealism is quickly splattered with blood. Or the hopeless romantic Jesse from “Before Sunrise” who, nine years later in the 2004 sequel “Before Sunset,” has a family and a best-selling novel and couldn’t be more miserable.

“Explorers” is about something secretly profound, Hawke says, and “it’s a metaphor, I think, for how all of us think. ‘Oh, if I can win the championship, if I could take over my dad’s business, if I could be a famous actor, my life will be fully realized.’ And invariably, whenever we pass one of these milestones — turning 50, turning 21, whatever it is — there’s this sense of disappointment of: is that all there is?”

“And yet I find it really beautiful,” says the actor, who turns 50 next month. “I do think that that has been the story of my life, and I’m probably drawn to stories like that.”

Hawke himself is the farthest thing from a bummer. He’s “excited all the time,” according to his old friend and frequent co-star Steve Zahn; he “has a big heart, he forgives, he cares,” says his “Before Sunrise” partner Julie Delpy; and he’s “always trying to find where he can improve, and he seems to put the art before himself,” says Juliette Binoche, who recently played Hawke’s wife in Hirokazu Koreeda’s “The Truth.”

Binoche notes how “he’s really male, but without imposing himself.” Hawke’s part in that film was subordinate to two strong women — Binoche and Catherine Deneuve — and perhaps a little underdeveloped on the page, “but he played the game.” Binoche is supposed to make a film in January, and “it’s very hard to find an American actor who’s willing to do a second part. Very difficult, because there’s something about wanting to be in the center.” In that way, Hawke “doesn’t have a misplaced ego at all.”

“He’s curious, which is not often the case with an actor,” says director Peter Weir, who encouraged Hawke to write scenes for his “Dead Poets Society” character and, essentially, become a co-filmmaker. Hawke has brought that writerly, collaborative spirit to screen projects ever since — in addition to forming his own theater company, writing novels and directing.

“He is an all-rounder, and multitalented, and can switch from one to another,” says Weir. “You know, he can fly fighters and bombers.”

Hawke was 18 when he made “Poets,” and he says the failure of “Explorers” prepared him for the next film’s success. “I’d put my hand in the fire and gotten so burned, that when people told me ‘Dead Poets Society’ was good — even when it was a hit — I was like, ‘No it’s not. Don’t care about whether people like it. Don’t care. Just do your work.’ ”

“So many of the things that we pray for, later in life we give thanks that our prayers were not answered,” he says of the abrupt end to his child-actor career. “I have felt blessed that what success I’ve had through the course of my life came in very small increments.”

Hawke’s recent successes have come more rapidly as of late, however. In 2018, he won accolades for playing another Christian extremist: the tormented Father Toller in Paul Schrader’s 2018 film “First Reformed.” Both Toller and Brown are radicals, true believers — holy fools.

“When I was a kid, my great-grandmother really thought that I was going to be an Episcopal priest,” he says. “She would talk about, ‘Have you had the calling?’ And I just prayed that I would not get the calling, you know. I did not want to do that. I wanted to be an artist.”

Hawke grew up in a “kaleidoscope” of Christianity; his Episcopalian parents divorced and married Christians in very different denominations. What was confusing to him as a kid led to an ecumenical curiosity that he now appreciates. It also makes the country’s Evangelical marriage to President Trump infuriating to him.

“I was raised by really serious Christian people, and I’ve always just been so disappointed in the leadership that we’ve seen,” Hawke says. “You sometimes wonder with these people’s politics if they’ve ever read the Sermon on the Mount, you know. John Brown was a nonviolent abolitionist for the first 51 years of his life, and what he came to believe is that, if you can read to people the Sermon on the Mount and they still will behave the way they are, then they have to be punched in the nose.”

Reexamining John Brown right now, he says, “certainly created for me an avenue to understand our past, and to see a relationship to justice, and to do something about it.”

In a barn-burning recruitment speech in the fourth episode of “The Good Lord Bird,” Brown talks about his decision to shed blood for his African American brothers and sisters, and he asks: “Do you think it’s a crime for a citizen to stand up and say, ‘Each and every one of us is imbued by our creator with certain inalienable rights? If that’s a crime, then the Declaration of Independence is a call for sedition and should be burned.” More spittle.

The series rings with eerie overtones of this year’s Black Lives Matter movement. Hawke notes how the Confederate statues he drove past in Virginia every day while filming are now covered in graffiti, or destroyed.

In a slight twist on his grandmother’s wish, he did feel called to play these men of radical, active faith — one fighting slavery, the other in “First Reformed” fighting climate change — in a time when oppression and injustice and fear seem to be winning. These characters offer a provocative alternative to our real-world religious leaders, or lack thereof.

“I think people have a real hunger and an appetite for exploring why we’re born, and why we die, and what our role is to live here together,” Hawke says. “But we don’t really see it reflected in our storytelling very much. No sooner do you mention the word ‘God’ than a lot of people skitter away from the dinner table, you know. I guess they’re scared they’re going to be preached to, or they’re scared they’re going to be told they’re wrong. But it’s such a valuable conversation to have.”

“I love both these characters,” he adds, “and this is really emblematic of this period of my life, of exploring these men of intense faith, and how our values can be manifested in our daily life. Because it’s really hard. I thought being a grown-up was going to be a lot easier and clearer than it’s been. Life is so messy, you know.”