Peter Capaldi’s incarnation of the Doctor has been publicised as being “trickier, fiercer, madder”, and even a “snarling beast”. A desire that’s been frequently bandied around by a lot of fans is for him to simply be “darker”. It’s a vague term when referring to anything other than a literal lack of light, because what constitutes dark characteristics for one might not scratch the surface for another. Is it just a case of toning down the more whimsical attributes, and introducing more solemnity to his character? Or should more elements of amorality be more frequently factored in to the actions he takes? Or should the Doctor start doling out extremely violent punishments to all enemies that confront him, elevating his own status to that of judge, jury, and executioner? OK, that last one was an exaggeration, but the point is that “dark” is a subjectively defined term in this context.
It’s a difficult balancing act where a character like the Doctor’s concerned, because at his core, he’s intended to be a beacon of pacifistic morality triumphing against the odds. He didn’t necessarily start out with such a heroic ideology. He began merely as an observer, who even once came close to taking a human life to assist in his and Susan’s escape from some cavemen in “An Unearthly Child”. But over the years it’s become one of his most defining traits, as was demonstrated in “The Day of the Doctor”, with the three Doctors uniting to save Gallifrey, as opposed to destroying it. And it’s crucial with a character that regenerates his face and personality each time he is mortally wounded that some significant attributes remain throughout the numerous changes.
The most notable instance of the Doctor taking a darker turn was with his infamous, self-proclaimed “Time Lord Victorious” act of rebellion in “The Waters of Mars”. When first arriving at Bowie Base One, the Doctor was desperate to leave as soon as he realised where he was, lamenting the fixed event in time of Captain Adelaide and her crew’s deaths, but resigned to its inevitability.
The Doctor’s decision to change this and save Adelaide, along with Yuri and Mia, was not just an act of defiance, but a demonstration of how perilously arrogant he could be. While his prior, sombre determination to allow events to unfold as the fixed point decreed was motivated only by a desire to maintain the precarious future of Adelaide’s pioneering descendants, his decision to alter the course of events was driven by a conceited view of himself as an embodiment of victory, rather than a regretful survivor, who dutifully, not triumphantly, brought the Last Great Time War to an end.
The Doctor’s attempt to prevent the inexorable death of Adelaide was provoked by his own impending, prophesised demise. It was not so much to save her for her own sake, but rather to selfishly prove to himself that the laws of time could be broken by his hand, and therefore his death could also be averted.
It was condemned by Adelaide, and to teach the Doctor the error of his ways; to demonstrate that causality was not his to trifle with, she committed suicide, thereby fulfilling the fixed point in time. The Doctor’s actions were symptomatic of a moral decline, and it’s the furthest down that slippery slope the character has fallen. But it still illustrates that crucial element of heroism. He may have behaved deploringly, but in the process he saved two lives that would have otherwise perished, and enabled Adelaide to see Earth one last time before she died.
There’s a limit to how far down this route the character can be taken, before surrendering what makes him identifiable as the Doctor. For instance, when he left the abhorrent Solomon to his fatal bounty with a sardonic departing quip, in “Dinosaurs on a Spaceship”, there were concerned outcries from some that it wasn’t in the Doctor’s nature to commit such an act of vengeance. It’s a difficult line to toe when exploring the more amoral facets of his character. It’s one of the reasons I very much doubt we’ll ever see the Doctor become the Valeyard on screen, despite the popularity of that notion, because once that occurs, the Doctor as we know him is lost. Transforming him into a fully evil incarnation would betray the character’s inherent qualities too much to be credible.
There’s also a danger in making the Doctor too abrasive, especially when he’s just starting out, as Colin Baker’s tenure demonstrated. He can still be, at heart, the same man, but if the outward persona is such that it obscures this too much, then the vast majority will not embrace him.
It’s why I believe expectations of how “dark” Capaldi’s Doctor will be should probably be reigned in somewhat. Hartnell’s Doctor was very cantankerous, aloof, and deceitful, but evolved into a far more amiable persona over time. He had the advantage of being the original template for the character, and so there was nothing to adhere to and no predecessors to compare to, which meant the boundaries could be pushed further than would be acceptable now. Of all the incarnations, it seems likely that Capaldi’s will have most in common with Eccleston’s (even their clothes reflect a similarly stark quality). His Doctor echoed some of Hartnell’s early traits, but not to as severe, nor as frequent, a degree. He could be cantankerous in his own way, and as equally insulting of human beings, but the requisite affability and beaming smile were still present from the outset.
I’m sure Moffat and co. are well aware that Capaldi’s Doctor must be liked by the fans, and so the extent to which he will be “trickier, fiercer, madder”, in all probability, will be a safe distance away from putting that in jeopardy. So, basically, if you’re highly anticipating him attempting to strangle Clara in the TARDIS during his first episode, you’re probably going to be disappointed.