Ncuti Gatwa Is the Newest ”Doctor Who.” Here’s How He Stacks Up.

With most TV shows, a major casting change is a dreaded event. But for fans of the long-running British series “Doctor Who,” big casting changes are expected, even anticipated. With the show’s latest Christmas episode, which premiered Monday on Disney+, we got acquainted with the newest Doctor, played by Ncuti Gatwa (“Sex Education”) — the 15th Doctor and the first Black, openly queer one in series history.

The arrival of a new Doctor, the show’s titular time-traveling, space-wandering alien, is always a buzzy occasion. But although the Doctor typically dies and is regenerated in the final minutes of some climactic episode, it is the one immediately following that truly establishes the new incarnation and what kind of flavor he or she will offer. These first full episodes with a new Doctor, including this year’s Christmas special, “The Church on Ruby Road,” can reveal a lot about how that Doctor’s tenure will go.

Here’s a look back at the first post-regeneration episodes of every Doctor since the show’s 2005 revival.

10th Doctor

Actor: David Tennant

First Full Episode: “The Christmas Invasion”

Writer: Russell T. Davies

First Words: “Hello. OK. New teeth, that’s weird. So, where was I? Oh, that’s right! Barcelona.”

After a successful revival in 2005 — with one tight season of Christopher Eccleston as the Ninth Doctor and Billie Piper as the Doctor’s plucky shopgirl companion, Rose Tyler — the series hit its stride with the next three seasons, starting with what is perhaps the best reincarnation episode since the series’s return, “The Christmas Invasion.” The episode was an auspicious start to the show’s new Golden Age, led by the showrunner and writer Russell T. Davies, with David Tennant as the Doctor.

The 10th Doctor delivers a rambling monologue full of queries about what kind of man he is, like Shakespeare refracted through some prism of intergalactic and temporal mysteries; but Tennant’s performance never allows any doubt that he knows who his Doctor is. In a scene near the end of the episode, Tennant’s Doctor firmly declares, “No second chances; I’m that kind of man,” while sending an enemy to his doom. The scene offered a preview of how perfectly Tennant’s Doctor would embody the duality of this hero through his three-plus seasons in the TARDIS — a masterly balance of stillness and chatter, heft and levity.

11th Doctor

Actor: Matt Smith

First Full Episode: “The Eleventh Hour”

Writer: Steven Moffat

First Words: “Legs! I’ve still got legs!”

It’s fitting that Matt Smith’s playful young Doctor (the youngest, in fact; Smith was just 26 when cast for the role) begins his tenure in a state of chaos, hanging out of a spinning TARDIS. Known for his fast talking, ebullient charm, the 11th Doctor is manic and wide-eyed in the manner of a precocious kid on a sugar high.

Crashing into the yard of a young Amelia Pond (Karen Gillan), who is independent and fearless but for the menacing crack in her bedroom wall, the Doctor arrives ready to step into the role of savior, though he is frazzled dealing with a resetting TARDIS and the aftereffects of his regeneration. Popping back into his TARDIS and promising Amelia he’ll be back in five minutes, the Doctor returns to find that little Amelia has grown up into Amy, who spent years waiting for a man everyone doubted was real.

Amy’s life is shaped around the absence of a magical man whom she clings to with a strangely unflappable faith. Her emotional arc with the Doctor is her learning to become independent from the Doctor. But the 11th’s moments of tenderness — as when he grabs the young Amelia’s hand, anticipating the danger — presage the familial relationship that the Doctor will develop with the older Amy and her boyfriend and future centurion husband, Rory (Arthur Darvill).

12th Doctor

Actor: Peter Capaldi

First Full Episode: “Deep Breath”

Writer: Steven Moffat

First words: “Kidneys! I’ve got new kidneys! I don’t like the color.”

In Matt Smith’s 11th Doctor and Jenna Coleman’s Clara Oswald, Moffat created another cute, flirtatious pairing for the TARDIS. The rapid-fire repartee and seamless synergy between the two got a harsh shake-up in the form of the Doctor’s regeneration into the 12th, played by Peter Capaldi.

This post-regeneration episode — which starts in Victorian London, where a dinosaur spontaneously combusts in the Thames, and ends as an organ-stealing cyborg tries to escape in a hot-air balloon made of human skin — was a brooding start for the 12th, whose tenure signaled a sharp tonal shift from the 11th’s. Capaldi’s Doctor is rude and pretentious, quick to condescend those around him and snap a quick “shut up.” He is more reminiscent of the Ninth in temperament: He shows more disgust and self-hate, and he is more haunted by his past actions. The 12th appears harsh on the surface but is no less dedicated than previous doctors to keeping everyone safe and alive at the end of the day.

Capaldi was 55 when cast in the role, nearly 30 years older than his predecessor, and the show appeared to spend the whole first episode trying to appease fans who might have opposed the big change. In fact, the episode baldly uses the out-of-place dinosaur as a symbol of this much older, out-of-place Doctor. It’s not the most elegant or subtle move, but Capaldi still manages to wring honest emotion from the symbol — something he would continue to do throughout his tenure as Doctor, especially in his later episodes. The 12th never showed the same humanity as the 10th and 11th did, but he had a streak of wisdom that neither could match.

13th Doctor

Actor: Jodie Whittaker

First Full Episode: “The Woman Who Fell to Earth”

Writer: Chris Chibnall

First Words: “Oh, brilliant!”

“Doctor Who” writers are all guilty, at one time or another, of throwing too much at the wall. But usually a fair percentage sticks. That was not at all true of Chris Chibnall’s writing during Whittaker’s disastrous run as the Doctor.

Usually the Doctor’s first episodes are more pared down; there’s no need to get over the top with a Predator-type alien who cheats at his human-hunting exam by using biotech to tag his human — and in the process installs DNA bombs in the collarbones of the Doctor and her new friends.

And speaking of friends, the episode is chock-full of them, overcrowding Whittaker’s performance, which remains at a steady level of earnestness and enthusiasm but fails to give nuance or variety. The first episode in a season-long attempt to replicate the more syrupy, wholesome quality of the old “Who” episodes, “The Woman Who Fell to Earth” can’t pull off any sense of menace or stakes, even when some characters begin dying.

14th Doctor

Actor: David Tennant

First Full Episode: “The Star Beast”

Writer: Russell T. Davies

First Words: “I know these teeth. … What? What? What?!”

In many ways, the return of Davies and Tennant after the exploding TARDIS disaster that was Seasons 11 through 13 felt like an emergency rescue maneuver. With a few keystrokes, Davies could have undermined or overwritten the 30-plus episodes of the previous Doctor’s arc, but the episode graciously makes a few nods — both comedic and sentimental — to the show’s attempt at telling more progressive and diverse stories during Chibnall’s run, joking at one point that the Doctor’s reversion to cis-male form was clearly a downgrade.

“The Star Beast” which begins the abbreviated three-episode return of Tennant’s 10th Doctor, now considered the 14th, is a refreshing return for the show. But even Davies’s captivating dialogue and engaging plots can’t make up for the tissue-thin logic behind this repeat Doctor regeneration.

That said, the performances, the reunion of these old faves, the digestible story and the addition of an absurd new alien to the Whoniverse in the form of the Meep (a Furby-type creature that speaks like Yoda), all make “The Star Beast” a solid entry in the “Doctor Who” catalog.

15th Doctor

Actor: Ncuti Gatwa

First Full Episode: “The Church on Ruby Road”

Writer: Russell T. Davies

First Words: “No way.” “You’re me!” “No, I’m me. I think I’m really, really me!”

Another Christmas premiere, “The Church on Ruby Road” is the first full outing for Ncuti Gatwa’s 15th Doctor. The plot — involving mischievous, baby-thieving goblins — gets too cutesy at times (a goblin musical number takes things too far), but it tidily connects the Doctor’s complex origin story with that of Ruby, a lively young woman and adoptee who is searching for information on her birth family.

Gatwa’s Doctor truly feels like a Doctor Who for the 21st century and a fitting follow-up to Tennant’s Doctor. The 15th is stylish and liberated, with a vibe that is sensual and unbuttoned; he’s a Doctor who seems much more at home than the others in his body. He is chipper but not frivolous, and he is capable of depth that isn’t limited to darkness. At one point in the episode, the 15th Doctor cries — full, drip-down-the-face tears — over the abduction of someone he just met and how that abduction has hardened those implicated in the loss. Gatwa’s Doctor shows a great deal of humanity, which isn’t always a given for the character, who often understands humans intellectually but closes himself off to a more comprehensive human experience.