There’s no denying the physical resemblance between the actor John Lithgow, who is sitting in front of me, and the author Roald Dahl, who he will soon depict on stage at the Royal Court. On one wall of the London studio where rehearsals are taking place is a collage of pictures of Dahl in his later years. In the opposite corner is Lithgow, here for another day of production prep, neatly squeezed into a wooden chair. “I was first sent the script mainly because I’m as tall as Dahl was,” Lithgow says, flailing his long limbs for effect. “And I do look a lot like him. Though I’m not sure I’m particularly proud of that part.”

Beyond their looks, the men share few similarities. Lithgow is genial, enthusiastic, softly spoken. The Dahl he intends to depict on stage starts off equally delightful. “He’s a charmer,” Lithgow says. “Our intention is for people to find him witty, delectable and endearing… Until they don’t.”

Lithgow is appearing in Giant, a play written by the director Mark Rosenblatt and set over a single summer lunchtime at Dahl’s Buckinghamshire country home. While some characters are fictional, the backdrop is true to life. It’s 1983 and The Witches, Dahl’s children’s novel, is about to hit the shelves – except there’s been a hiccup. Dahl has recently published a review of God Cried, a book about the 1982 Lebanon War in which Israel invaded Lebanon, in a literary journal. His passionate pro-Palestine prose is peppered with antisemitism. In it he refers to Jews as “a race of people” who had “switched so rapidly from being much-pitied victims to barbarous murderers”. And he describes the US as being “so utterly dominated by the great Jewish financial institutions” that “they dare not defy” Israel. The play fictionalises a meeting between Dahl and envoys from his UK and US publishers, both Jewish. Their communal task is damage control. Rosenblatt, the playwright, had become “alarmed, as a British Jew, by how openly antisemitic language and stereotyping was blurring with meaningful, constructive debate around Israel and Palestine,” he told me, and thought Dahl’s tale an effective vehicle to explore the problem further. Lithgow goes on, “It’s like a psychological suspense thriller. But it’s people sitting around for a Sunday luncheon. I’m expecting audience gasps.”

This is familiar territory for Lithgow. “I seem to be the go-to person for perverse and contradictory characters,” he says. “The extreme of that is the Trinity Killer in [HBO’s] Dexter: a man who professes to be benign and ordinary, but who has this ferocious compulsion to butcher people.” Why does he get these roles? “Well, I’m a pleasant, ordinary, slightly boring man who plays crazy parts. People come to me if a character has two antithetical sides. I loved playing Churchill in The Crown for that reason. A man full of contradictions: charming and appalling. The same goes for Dahl.”

Giant was written before the events of 7 October last year. “That radically shifted the entire production,” Lithgow says now, “though every word of the script stayed the same.” He goes on, “This play is set a year after the 1982 Israeli incursion into Lebanon: the siege of Beirut, the massacres of Sabra and Shatila. All those big pieces of history were very familiar to everyone 40 years ago. Less so when work on this play started. But now, with current events? It has made the play…” He pauses. “It needs to do much less educating. There is already a clear context for it. In October last year, my first reaction was: this subject is too white-hot now. I didn’t think we could do it. Things were too inflammatory. Thankfully, the team saw that it deepened the play.”

The Royal Court itself was dogged by an antisemitism scandal in 2021: a fictional, manipulative billionaire in a new production, the play Rare Earth Mettle, was to be called Hershel Fink. The theatre eventually apologised and the name was changed, but ill-feeling lingered. “It caused a huge controversy,” Lithgow says. “That kind of story can affect the culture of an entire institution and I think it’s probably made them nervous. But this is the Royal Court: it’s controversial and bold. It’s perfectly typical they went right ahead to do this play. They probably saw it as a way of addressing that recent history.” (In 2022, the Royal Court put on Jews. In Their Own Words, a play written by the journalist Jonathan Freedland that used verbatim interviews to “expose the roots and damning legacy of antisemitism in Britain”. Many saw it as a kind of penance.)

Lithgow has been consumed by Dahl’s complex character for nearly two years, since Giant’s director Nicholas Hytner forwarded an early draft of the script. The pair are old friends. Lithgow committed to the part long before the Royal Court agreed to put on the play, and before even his own availability was confirmed. “I loved the daring of it. It was grappling with subjects as volatile as English antisemitism and Israel-Palestine, in a penetrating way, while also exploring Dahl intimately: his fascinating relationship with Felicity Crosland, with whom he’d had a long affair during his marriage. There’s the loss of one child [Dahl’s eldest daughter Olivia, one of five Dahl children, died of measles encephalitis when she was seven], another severely compromised [Dahl’s son Theo was injured at four months old when his pram was hit by a taxi], in two great tragedies, alongside the fact he’s a genius at delighting kids. A man who bears huge grief and is an outsider; who speaks compellingly about Israel/Palestine, alongside espousing deplorable beliefs. That’s red meat to a tiger for a character actor like me.”

Lithgow started acting young. He was born in 1945 and raised in a theatrical family, first in Rochester, New York, then in Ohio, where he spent his teenage years. His mother was an actor, his father a theatre director and producer. “Shakespeare was his speciality,” Lithgow says of his father. “While I was aged between seven and 12, he produced every single one of Shakespeare’s plays, the first American to do so. By 17, I worked as an apprentice for another of my father’s companies, playing tiny character parts.”

Despite wanting to pursue a career as an artist, he fell into the theatre gang soon after arriving at Harvard. “I was already a seasoned actor,” he says, “and became something of a campus star. I played Gloucester in King Lear at 18. It left people asking: “Where did this guy come from?’ I was so much better than [the man who played] Lear, a professor who took all the good roles.” There’s no arrogance in his tone, just a certainty in his long-since-proven talent. When Lithgow later played Tartuffe, the Harvard Crimson ran a glowing review. “If John Lithgow weren’t the star of this show it wouldn’t be worth seeing. He is. It is. See it. When you grow up you can tell people at cocktail parties you saw him before he was. Which won’t be true, actually, because he is already.”

“I was a big fish in the pond,” Lithgow says. “And that feedback at a success-oriented place like Harvard? It was a no-brainer that I’d act.” In 1967, the year after he graduated, Lithgow enrolled on a course at the London Academy of Music and Dramatic Art (Lamda) on a Fulbright grant. He was desperate to cross the Atlantic. “I’d long sat around listening to Olivier’s Othello on LP records,” he explains. “Robert Stephens and Maggie Smith and Much Ado About Nothing. I was infatuated with English theatre. And here, I found out more about English history and literature than I ever had before. Suddenly I knew where Kent was.”

When he returned to the US, Lithgow spent a year working at his father’s theatre. “But it was odd to be in a resident company with your dad as boss when playing major roles. I had to go and do it myself. In 1970, I headed to New York to make it. I was out of work for two years straight.” He worked at a radio station and drove a cab. “You gave all the legroom to passengers,” he says. “I’m just too tall. It practically crippled me.” Lithgow had married at 21 having met his first wife while performing together during a college vacation. “Nobody was hiring me to act. I relied on my wife’s teacher’s salary.” Deflated, he accepted a directing post in Baltimore. “Then two weeks later I finally got an offer I really wanted” – to become a member of the resident company at a prestigious regional theatre. “My second production there was a new play from England, The Changing Room, by David Storey. It was a terrific play: 22 men, 15 of whom were rugby players. It all took place in their changing room.” It was a hit, transferring to New York months later. Lithgow went with it. “I won a Tony award for it. And BAM!” he yells, “I was a known actor. I’ve not been out of work since.” There have been benchmark parts, he says, including 3rd Rock from the Sun, which involved him playing an alien for a decade. He’s won two Tonys, six Emmys and two Academy Award nods. Theatre, TV and film. “But you get in front of young people and mention the word Shrek [he voiced Lord Farquaad in the film] and they go berserk.”

Lithgow was based in New York when he met his now wife Mary Yeager, a professor at UCLA. While on a shoot in Texas, in 1980, the couple were set up by a mutual friend. “My first marriage had broken down after 10 years,” he says. “Mary’s also had. She knew of our lunch date, but nobody had told me. There I was, sweaty, in borrowed tennis gear. She looked a picture. It was love at first sight.” He laughs. “Professors and actors are not supposed to marry. Our lives are so incompatible.” After two years of “transcontinental tug-of-war” Lithgow relented, and headed to LA.

Yeager is retired. Lithgow, who turns 79 next month, has no such plans. Earlier this year he was shooting in New Zealand. Then filming with Olivia Colman in Amsterdam. After three months on stage in England, another movie set awaits. “It’s much harder on Mary than me,” he says of his schedule. “I’m going off to do fantastic things with fabulous new friends. It’s exhilarating and gives me life.” They’ve found a better rhythm in her retirement. “But there are stretches where we’re apart, and it’s hard. Currently we have three phone calls a day with our eight-hour time difference. All intricately timed. We’re still working on it, basically.”

Beyond the Israel/Palestine conflict, Giant addresses another question: can we separate the art from the artist? In the script, Dahl raises this point himself. “I’ll quote it for you,” Lithgow says, before dropping a register. “‘If you feel all these terrible things about me, can you no longer read my books to dear Archie?’” Dahl asks this of one of his Jewish American lunch guests, in reference to her son. “That is a wonderful thing to put forward, from Dahl himself. It’s an ongoing argument. I could list 20 people caught in that dilemma right now, in their public perception. Brilliant people with views that appal.”

In Giant, the worst of Dahl’s recorded antisemitism is repeated, including atrocious lines from an interview in which he said, “Even a stinker like Hitler didn’t just pick on them for no reason.” In December 2020, the Dahl family posted an apology on the estate’s official website, acknowledging the “lasting and understandable hurt” his “prejudiced remarks” caused. Some of his books have been rewritten to remove offensive language. “It’s an embarrassing truth for English culture,” Lithgow says. “One that is hard to tackle.” But his stories remain firmly in the canon. Audiences will leave Giant asking whether that should change.

Lithgow isn’t inclined to wade in on the issue, cautious about drawing attention to his own politics. But he has written books of satire that skewer Donald Trump, about whom Lithgow is uncharacteristically blistering. “I do think Trump is an abhorration,” he says. “He so appals me. Still, I didn’t set out to take him down. I have a delightful literary agent for whom I produce practically nothing. He was bugging me about writing another book…” The previous year, Lithgow had done a turn at Central Park’s Delacorte Theater. Dressed as the recently disgraced ex-White House National Security adviser Michael Flynn, he performed the Major General’s song from The Pirates of Penzance, rewriting the final verse. He bursts into song: “When President Obama made me head of all things Clandestine / He realised he’s brought to life a governmental Frankenstein / But then I made a killing in case of public pillory / By shouting LOCK HER UP in my harangue opposing Hillary…”

He goes on, “When I sang this to my agent, he suggested I write something similar. So I wrote three books, all bestsellers. Then suddenly I was perceived as political. I’ve always had my politics. I’ve made no bones about it. I campaigned for Hillary Clinton in Ohio. But I’ve never been on the frontline. I’m no Susan Sarandon or George Clooney. I never felt I had the heft for my opinion to be weighty and important, to change anyone’s mind. I’m a little uncomfortable with actors taking that role.” Why? “Well…” He sighs. “We’re in the acting business: the job is pretending to be other people. I think coming out of your shell and going public with your views is different. I should be malleable in the public’s perception.” One review of Dexter saw Lithgow labelled “‘a bland blob of a man’, which I took as a great compliment, although I’m not sure how it was intended.”

Lithgow believes this approach allows him to inhabit complicated characters, such as Dahl, with empathy. When he told friends about Giant, some worried for his safety. “But the play offers articulate arguments on both sides. No matter what your belief is, you’ll hear your case stated. And it’ll wrench your sensibilities around while you go.” For now, at least, Lithgow is still in its throes. “I’m a little worried that I’m defaming Dahl,” he suggests, “just because… of course, we are speaking some truths about him that need to be told. But it’s going to be quite scandalous, I think. It takes a lot of courage from us all to do this play. It’s going to confront audiences in ways they won’t expect. It gives me anxiety.”

It would be easy for Lithgow to play Dahl as a monster. Instead, he aims to uncover a would-be villain’s humanity. “We all have these contradictory qualities,” he says. “It’s my job to illuminate that. I apply the same basic rules to daffy comic roles and horrific parts in psychological suspense thrillers. Embody the character. Try to explain them to people, so they make emotional sense.” This perspective, he says, can be limitless. “Take Trump. I despise all he stands for, yes, but I also feel sorry for him. He’s a terribly unhappy man who lives with demons and carries such a weight on his shoulders. I want him defeated, politically, in this next election. But to see another human destroyed? As an actor, you always have to be on the side of the character you’re playing. Sympathetic to him or her, regardless.” He glances over, again, to those Dahl portraits. “That outlook on the world can’t help but shape how you see things.”

Giant is at the Royal Court until 16 November (royalcourttheatre.com)

Stylist Hope Lawrie; photographer’s assistant Lily Miles; grooming by Dani Guinsberg using Vichy skincare; thanks to Airspace Locations