“Give-ING! That dress is giving!” said Ncuti Gatwa with a burst of unbridled laughter. The newest Doctor Who had been shooting the same scene for several hours in Cardiff, Wales, where hangar-like spaces were teeming with crew and filled with sets and equipment for the show. (Yes, Whovians, the TARDIS was parked nearby.) Now, at the director’s request, the new Doctor was improvising.

Gatwa (whose first name is pronounced “Shoo-ti”) laughs a lot, often at himself. “Why do I keep moving this footstool?” he asked a few minutes later as he tried to get into position for yet another take. “Because the art department isn’t here to do it for you,” teased Varada Sethu, who joins the Doctor and his current companion Ruby Sunday (Millie Gibson) for some adventures in Gatwa’s second season. “I have to do everything myself!” cried Gatwa in a mock-tragic tone, before another eruption of mirth.

Born in Rwanda and raised in Scotland, Gatwa, 31, made his name playing the effervescent Eric in Netflix’s “Sex Education.” But the lead role in “Doctor Who,” a British institution about a time-traveling alien and his human companion that has been a BBC stalwart for 60 years, has taken him to another level of fame.

The show — which first ran between 1963 and 1989 — was revived in 2005 and today has an exceptionally diverse, intergenerational fan base. But the current season, which ends on June 21, has ushered in a new era for the show, with Disney+ now a co-producer alongside the BBC and Gatwa the show’s first Black lead actor, with a distinctly fabulous vibe.

The pressures and expectations surrounding these firsts aren’t lost on Gatwa, who grew up in a working class home in Dunfermline, Scotland. “‘Doctor Who,’” he said, “is something I remember as almost over our heads, something we knew was important culturally, like the royals.” His audition “was lovely, but I didn’t think I was going to get it,” he said. “British casting has taken a long time to diversify — why would it be now, and why me?”

The anxiety he felt about “getting it right, living up to the amazing people who have done this role,” lasted through filming the first season, Gatwa said. “Gradually, it became clear to me that there isn’t a mold you need to step into to portray the Doctor,” he said. “It can come out of you naturally.”

Russell T Davies, who is back as the “Doctor Who” showrunner after masterminding the 2005 reboot, said that although the increased production budget had allowed for more special effects, “it’s still me sitting with a script, making good dialogue for actors,” he said.

In the past, he added, the Doctor “has been marvelously inexpressive and enigmatic and alien, and great actors have done that very well.” But in 2024, “I want a young audience watching, and they talk about their emotions, express their emotions in a healthy way.” Then, “along came Ncuti, who is one of those actors who pour with feeling,” Davies said. “When he is sad, tears pour from his eyes; when he is happy, that smile lights up the universe.”

Viewers who have watched Gatwa’s Doctor battle the Maestro (Jinkx Monsoon), perform a song and dance number, stand on a land mine for an entire episode and suit up in Regency attire for a “Bridgerton”-themed episode, are likely to agree. He “truly feels like a Doctor Who for the 21st century,” wrote Maya Phillips in The New York Times. He is “stylish and liberated,” she added, “with a vibe that is sensual and unbuttoned; he’s a Doctor who seems much more at home than the others in his body.”

The companion’s role is usually “to have the human qualities the doctor lacks,” Gibson said, but the relationship between this Doctor and the companion she plays feels different. “Ruby’s youth allows him to let out his inner child,” she said. “You see that Ruby and the Doctor really care for one another; the way they communicate and laugh is very loving.” Gatwa “is a force of nature, just magic,” she added. “He has this aura about him that everything can feed off.”

On a busy day in April, Gatwa, dressed in a flower-embossed red shirt, was demonstrating Gibson’s force-of-nature theory in an interview, gesticulating, laughing uproariously and attempting to eat avocado toast while talking about his past and his career. Even an interruption by an assistant bearing forgotten contact lenses was greeted with incommensurate joy: “Yay! Oh, my God, yessss! Hallelujah, aahhhh, great!”

“You need glasses,” she told him. “I know, but I’m so vain,” he said plaintively. More laughter.

Born in Kigali, Rwanda’s capital, Gatwa was 2 when his parents — a journalist and a bank manager — moved to Scotland with their three children to escape the 1994 Rwandan genocide. Largely raised by his mother, he took drama in high school and had an aha moment playing Commander Khashoggi in his school production of “We Will Rock You.”

He roared with laughter. “I must have been SOOOO bad! But at that point, I was like, thisssss is what I want to do.”

Gatwa said that his family “were one of three Black families we knew in, like, all of Scotland, which I both noticed and didn’t notice.” But he didn’t doubt, he said, that there would be a path for him in the theater: “I always saw a Black actor working.”

He spent three years at the Royal Conservatoire of Scotland (“I LOVED LOVED LOVED it”), and then a post-graduation year with the Dundee Repertory Theater (“Greek drama to Agatha Christie”). Jobs followed playing Mercutio in “Romeo and Juliet” at the Home theater in Manchester, England, (“where I saw a ghost — I swear”), and then roles in “Shakespeare in Love” in the West End and in Emma Rice’s “946: The Amazing Story of Adolphus Tips.”

Gatwa “is obviously one of the most beautiful, charismatic people you will ever meet,” Rice said in a video conversation. “But he also has phenomenal emotional depth he brought to every rehearsal and every performance, an incredible work ethic and an amazing ability to talk to the audience.”

After “946,” Gatwa was suddenly out of work and broke, temping at Harrods, a department store, to make ends meet. He was in his eighth month of sleeping at his best friend’s apartment when he got the part of Captain Jack Absolute in a production of Richard B. Sheridan’s “The Rivals.” Then came the call to audition for “Sex Education.”

When he got the job, he said, his primary thought was that he could pay his overdue bills. He had hardly done any screen work before, but discovered that the show, with its ensemble cast, didn’t feel too different from a theater group.

“I had never really met someone like him before, so full of life and experience and so buoyant,” said Emma Mackey, one of his co-stars. “He took up that space offered and grew into it; we were an alliance, but Ncuti really lead us in that frame of mind.”

Ben Taylor, the lead director for Season 1, said that at the first table read, “there was a sigh of relief and also confidence around the table, because Ncuti knew the show possibly before the show knew itself.”

Gatwa said that playing Eric, a lovable gay teenager from a religious British-Nigerian family, over four seasons taught him to be braver. “Eric was so dedicated to his authenticity, living his truth. That has permeated into my life,” he said.

After “Sex Education” ended, Gatwa played supporting roles in “Masters of the Air” and “Barbie,” and one day texted his agent, saying he would “love to play Willy Wonka or Doctor Who.” She replied that the “Doctor Who” casting director, Andy Pryor, had just asked him to audition.

“It sounds like a showbiz story, but the last person we saw was Ncuti — and bang!” Davies said. “I knew then and there that was the man.”

Gatwa said that he and Davies didn’t have many discussions about his portrayal of the Doctor. “This is a character that is constantly born again, with fresh eyes,” he said. “There is an element of innocence within the Doctor. For me, that’s where his curiosity comes from, the confidence to explore the unknown in the way kids do.”

Asked whether he consciously incorporated more L.G.B.T.Q. elements into Gatwa’s first season, Davies pointed out that he has been putting gay characters onscreen for around 30 years. “We never had a sexuality meeting,” he said with a laugh. “And the Doctor is an alien, of course — he’s not Ncuti Gatwa, and I think human labels barely apply to him. He loves Ruby with all his heart. He doesn’t care what gender people are.”

Gatwa had another take. “I feel like ‘Doctor Who’ has always been a bit camp,” he said. “I mean, it’s a time-traveling alien in a British police box!”