Every time Doctor Who's hero regenerates, we get to see a fresh twist on a character that's been around for over half a century. But even as they have made the role their own, the four actors to play the Doctor in the 21st century have also paid homage to the show's legacy by echoing their predecessor's performances. Here are the many ways the most recent Doctors have been inspired by their forebears.
The Ninth Doctor
Unsurprisingly, given just how much of a clean break Russell T. Davies' revival of Doctor Who was from its classic incarnation, Christopher Eccleston's performance as the Ninth Doctor is the one with the least obvious echoes to Doctors past. If anything, his Doctor very forcibly denies his own history: He isolates himself from other people in a way his past selves rarely did. And he eschews many of the affectations of his past, to present a more down-to-Earth version of the Time Lord, rather than an eccentric oddity, even down to his clothing. But that's not to say that the Ninth Doctor doesn't share some similarities with his past incarnations.
The biggest callback to past Doctors comes in the way the Ninth Doctor starts out being largely disdainful of people he thought below himself, like Mickey (or humanity in general) — an approach to The Doctor that was most keenly on display in the first and seventh incarnations, and one which likewise similarly developed into a softening and warmer view of the people around them, as they spent more time with their respective companions.
But perhaps most surprisingly, given their tonal diametric opposites, Eccleston's Doctor also shared a lot of similarities to Jon Pertwee's era. This was not just in the two eras' Earth-bound storytelling, but in terms of their personalities. They share a brusque, anti-establishment, know-it-all attitude, that casts them both as people out of place in their surroundings — something that made Pertwee stand out as an outlandish dandy, but gets twisted, with the Ninth Doctor, into a darker, more rebellious persona.
The Tenth Doctor
By the time David Tennant joined Doctor Who, the show was more secure, and more able to acknowledge its past eccentricities — and unlike his predecessor, the Tenth Doctor was much more open in his echoing of one past Doctor in particular: Peter Davison's fifth Doctor.
As the "young" Doctors of their respective eras, the Tenth and Fifth Doctor shared not just emotional similarities — a manic joie de vivre, an abhorrence of violence, an joyous appreciation for the beauty of the world and people around them and, yes, a penchant for rapidly dashing around everywhere with almost breathless excitement — but some similar physical affectations, too.
Both Doctors have a fondness for the "hands in pockets" stance that makes them look disarmingly casual in tense situations. Plus liberal use of "brainy specs" that they pull out when they want to appear even smarter than they're letting on. They even share a habit of letting their voice break when they raise their voices in anger or excitement. As the Tenth Doctor tells his past self in "Time Crash" (which you can see above), these are both incarnations that reflected The Doctor's idea to cast aside a more "mature" sense of self, and live a little youthfully.
However, in times of darkness, the Tenth Doctor has strayed from his close connections to his fifth self, with a display of righteous fury that puts him more in line with his sixth or seventh incarnations. He's also prone to reveal a dark streak of arrogance, that casts himself as someone above all else, the ultimate arbiter of time and space. His almost petulant, selfish streak in his final days, along with his desperation to avoid regenerating and moving on, bring him in line with the more manipulative aspects of the First Doctor, at times.
The Eleventh Doctor
On a surface level, the Eleventh Doctor shares a lot of the youthful personality of his immediate predecessor — a zany, childlike sense of joy and excitement, that might similarly put you in mind of the Fifth Doctor. But Matt Smith's physicality and youthfulness just conceal a weary old soul, that has much more in common with the Doctor's earliest incarnations. That combination of a youthful body and elder, almost professorial, mind was an intentional link on Smith's part to the Second Doctor in particular. The actor had noted, on several occasions, that one of the first Doctor Who stories he watched after being cast, having grown up without the show on television, was the classic Patrick Troughton story "Tomb of the Cybermen". This was an inspiration that would draw the two Doctors together throughout the Eleventh Doctor's era.
Much like the Second Doctor's goofy behaviour, the Eleventh Doctor's childishness — a love of nonsense words, physical awkwardness, even a disposition that made him get on better with children rather than adults — is a mask for a keenly intelligent and calculating person. This disarming technique helps trick the foes of both of these incarnations of the Doctor into underestimating them — but sometimes, the exuberant silliness is as much a display of their exuberance as a mask for their real intentions.
The Eleventh Doctor, of course, also has a deep, abiding adoration of hats. And that's an affectation he most definitely shares with the Second Doctor, who on several occasions dons some elaborate and rather silly headgear as part of his "clownish" act, just as the Eleventh does with his beloved fez.
Like the Tenth Doctor, the Eleventh's silliness disguises a dark streak, except that his has much more of a connection to the manipulative trickery of Sylvester McCoy's incarnation. Just as the Seventh Doctor pokes and prods at Ace's life, the Eleventh Doctor's meddling in the life of Amy Pond is a fundamental part of his journey on the show — and reveals a manipulative cunning, far beyond his youthful appearance.
The Twelfth Doctor
It's interesting to note that as the modern incarnation of Doctor Who has gone on, its different characterisations of The Doctor have more openly emulated the Doctors of the classic series. And while Peter Capaldi's incumbent Doctor was lauded as a change of pace from his predecessors in David Tennant and Matt Smith, his Doctor has more echoes of the show's past than almost any other.
If the Tenth (and in some ways Eleventh) Doctors were meant to show the character internally reverting to a more youthful persona in response to the dark events The Doctor had endured, the Twelfth is an open acceptance of the maturity The Doctor displayed in his earliest incarnations. This maturity also pairs itself with an brusqueness that keeps him distant from the people he encounters on his travels. He makes an intimidating presence, much in the vein of the First and Fourth Doctors.
The Twelfth Doctor's intimidating nature also draws comparison to the arrogance of the Sixth Doctor, or the calculating schemes of the Seventh, which reflects Capaldi's oft-repeated claim that his Doctor channels almost every past incarnation of The Doctor. Although he has his own distinct personality, the Twelfth Doctor has an amalgam of his predecessor's traits and characteristics on display that make him more of an echo of The Doctor's past than any previous incarnation. Even his dress sense borrows from the sartorial style of Doctors past — whether it's the clean, almost magician-esque look he wears in season eight, reflecting the style of the Third Doctor, or the more dishevelled "cosmic hobo" look, akin to the Second Doctor, he's been wearing in season nine.
But in terms of affectations, the Twelfth Doctor shares the most in common with the Doctor of Capaldi's childhood: Jon Pertwee. The Third and Twelfth Doctors find common ground in a love of invention, and occasionally, even a penchant for martial arts. Primarily, however, the two are linked through a sense of flamboyance — and frequent love of posing and dramatic pointing — that is an expression of their softer side, after a companion chips away at the more aloof exterior.