The Twelfth Doctor was the thirteenth incarnation of the Time Lord known as the Doctor, and the first of a new regenerative cycle given to him by the Time Lords.
When the Teselecta helped fake the Eleventh Doctor's death by being shot by an impossible astronaut, River Song informed Amy Pond and Rory Williams that it was the Doctor's inability to regenerate into his next life that actually killed him. (DW: The Impossible Astronaut)
After fighting in the Siege of Trenzalore for 900 years, (EBook: Tales of Trenzalore: The Eleventh Doctor's Last Stand), the Eleventh Doctor, facing extermination from the Daleks in his old age, was ready to accept that he had reached the end of his life. Unable to accept his death, Clara Oswald appealed to the Time Lords to intervene and the Doctor received a new regeneration cycle. After using his regenerative energy to destroy the Daleks mother ship, he returned to his TARDIS to complete his regeneration.
Suddenly changing in a flash before Clara's eyes, the new Doctor voiced his surprise at having new kidneys. The TARDIS then began shaking violently, and the Doctor implied to have forgotten how to pilot his ship, much to a shocked Clara's dismay. (DW: The Time of the Doctor)
Crashing in pre-historic Earth, the TARDIS was chased and subsequently swallowed by a female Tyrannosaur; when the Doctor brought the TARDIS to 1890s London, the dinosaur was accidentally brought along with it.
After the TARDIS was spat out, the Doctor, in a severe bout of post-regenerative trauma, acted very wild and irrationally. He peeked out of the TARDIS door, shushed Strax, slammed the door shut momentarily, and then finally crept out of the TARDIS, trying to identify him as one of the Seven Dwarves. Unable to remember names or faces clearly, he sputtered at the sight of the Paternoster Gang, before being joined by a frazzled and annoyed Clara, trying to keep some degree of control on his livid and maddened state.
Though put to bed to stabilise, the Doctor soon awoke and, grabbing a piece of chalk, doodled all over the bedroom with strange equations. Hearing the dinosaur in pain, the Doctor climbed out onto the rooftop and left on horseback when he saw the T-Rex was being burned to ashes. Deciding to investigate, but still suffering a degree of post-regenerative stress, the Doctor wandered the streets of London. Talking to a passing tamp, the Doctor examined his new facial features, taking particular note of his new eyebrows, as well as his new Scottish accent, before trading in his previous incarnation's favorite watch for the tramp's coat and gloves.
Seeing an ad in a newspaper that seemed to be a message from Clara, the Doctor infiltrated a suspicious restaurant, where he and Clara learned that time traveling Clockwork Droids, under the leadership of the Half-Face Man, had been harvesting humans to repair themselves and reach the Promised Land. Trying to speak on peaceful terms, the Doctor snapped the Control Node out of his illusion of the Promised Land by revealing the true state of his existence. Conflicted and unsure, the Half-Face Man fell out of his escape pod, either jumping or having been pushed by the Doctor. (DW: Deep Breath)
He briefly left Clara behind to help his previous selves place Gallifrey in a pocket universe at the end of the Last Great Time War, (DW: The Day of the Doctor) redecorate the console room and settle on a new outfit.
Returning for Clara, the Doctor spoke of the suspicious way Clara had met him in his eleventh incarnation, only for Clara to likewise voice her uncertainty of the Doctor's identity and asked to be returned home. Attempting to return Clara home, the Doctor ended up in Glasgow by mistake. However, Clara decided to go out for coffee with the new Doctor after the Eleventh Doctor called her and encouraged her to help the Doctor through his regeneration. (DW: Deep Breath)
Encountering A Good Dalek
Leaving Clara behind in Glasgow to get coffee, the Doctor got distracted, went off in the TARDIS on his own and ended up saving a Combined Galactic Resistance fighter pilot named Journey Blue from a Dalek Saucer attack, though left her brother behind in the explosion. After prompting her into asking nicely, the Doctor returned Journery to her command ship, the Aristotle, where Colonel Morgan Blue introduced him to a Dalek that had developed a fault and turned good.
Returning for Clara, three weeks later from her perspective, the Doctor asked her if she thought he was a good man, a question that Clara found herself unable to answer, and returned to base to help the Dalek. Joined by Journey and two other soldiers named Gretchen Carlisle and Ross, the Doctor and Clara used a Molecular nanoscaler to miniaturise themselves and enter the Dalek — whom the Doctor nicknamed "Rusty". After losing Ross to the Dalek's antibodies, the Doctor discovered a radiation leak from within the Dalek and learned that Rusty had turned good after seeing a star being born. Following the radiation, the Doctor discovered damage to Rusty's power source was slowly killing him, and repaired the damage with his sonic screwdriver.
However, fixing Rusty's power core resulted in the malfunction that turned Rusty good to be reversed, with Rusty's destructive nature returning, and causing Rusty to go on a killing spree, as well as send a distress beacon to summon the Daleks to the rebels' base. After getting slapped and lectured by Clara for his apathy, the Doctor realized he could turn Rusty good again by reawakening his memory of the star being born.
Instructing Clara to find a way to restore Rusty's memories of the star, the Doctor made his way to the Kaled mutant within Rusty to mind linked with him, causing Rusty to see the Doctor's hatred of the Daleks and destroy the Daleks that had responded to his distress beacon. Leaving to continue his crusade against the Daleks, Rusty commented that Doctor would have made a good Dalek before both of them left. After declining Journey's request to travel with him and Clara, the Doctor returned Clara home, both still unsure if the Doctor was a good man, but with Clara convinced he was at least trying to be one. (DW: Into the Dalek)
Becoming alerted to a creature that disguised itself as a motorway to consume planets into other dimensions, the Doctor summoned Clara to assist him, but was surprised when the creature disappeared, unaware that Clara had tricked the creature into consuming itself. (DWA: Road Rage)
Deciding to give Clara the choice of their next destination, the Doctor took her to Sherwood Forest to meet Robin Hood, though the Doctor remained skeptic of Robin's existence. He was proven wrong immediately on arrival when Robin shot his TARDIS with an arrow; however, he remained adamant to prove Robin Hood and his Merry Men were fakes.
After participating in an archery contest for a golden arrow, the Doctor, Clara and Robin were caught by the Sheriff of Nottingham, who had allied with alien robots disguised as his knights. Escaping, the Doctor found out that the robots were trying to reach the Promised Land, but lacked sufficient gold to repair their engine. Believing Robin was also a robot, the Doctor was captured by the Sheriff as Clara and Robin escaped through a window. Leading a revolution in the Sherriff's dungeon, the Doctor was informed by the Sheriff that Robin Hood was not a robot, just as Robin came to his rescue and defeated the Sheriff. Assisting Robin with Clara's help, the Doctor helped launched the golden arrow into the ship to allow it to escape velocity and explode harmlessly in space.
The Doctor finally acknowledges Robin Hood as a genuine person, not a myth. (TV: Robot of Sherwood) At the end of the adventure, Robin, having learned about the Doctor's origins and story, noted that the two of them were not so different from each other, both of them being people born into status and privilege and having given up both to live the life of an adventurer in order to fight injustice. (DW: Robot of Sherwood)
The Doctor and Clara used a goo bomb to foil the Sibro's attempt to weaponise a Conlanian clock tower, (DWA: Chime Time) orchestrated a ceasefire in a war between anthropomorphic cats and dogs by allying them against an army of alien fleas that planned to attack every planet in the universe, (DWA: Once Bitten) and helped the World Brain find a new way of life after crash landing on it's factory planet. (DWA: Crash Landing)
A sarcastic man armed with an acerbic wit and a brutal honesty, the Twelfth Doctor was dark and at times manipulative, willing to place his companions in danger if it meant appeasing his curiosity (DW: Deep Breath) and leaving them out of the details in his plans. (DWA: Chime Time) However, if he believed the situation was too dangerous for them, the Doctor would send his companions to the safety of the TARDIS while staring down the threat alone. (DW: Listen)
Despite coming across as uncaring, he would fight to protect those in his care, and would react with devastation if harm befell them. Such was his reaction to the death of a female Tyrannosaurus rex that had been inadvertently dragged through time by the TARDIS. (DW: Deep Breath) However, for the most part, this Doctor was far more detached than his immediate predecessors and occasionally callous, reacting with indifference during his first encounter with Journey Blue, who had just lost her brother. (DW: Into the Dalek) He also acted indifferent to the apparent death of Saibra, causing Psi to ask him if he called himself the Doctor due to professional detachment. (DW: Time Heist)
The Twelfth Doctor showed even less restraint than his predecessor, and would get frank and physical with his enemies. (DW: Deep Breath) However, he often skirted a jagged line between right and wrong values due to a conflicted sense of morality and the struggle with his inner darkness. He sometimes voiced preconceptions about his enemies or human nature, but might find them maligned and questioned his own judgement afterward. (DW: Into the Dalek)
Though he retained a respect for humanity, the Twelfth Doctor would insult them for being slow minded and violent, dubbing Earth the "planet of the pudding-brains". (DW: Deep Breath) He expressed a strong dislike for soldiers, because of their hidebound nature, (DW: Into the Dalek) and was easily annoyed by swashbucklers who did not take things seriously. (DW: Robot of Sherwood) He also claimed to dislike karaoke, mime, (DW: Deep Breath) and babysitters. (DW: Into the Dalek)
Unlike his immediate predecessor, the twelfth incarnation was not a affectionate Doctor, failing to return Clara's hugs, (DW: Deep Breath) and being momentarily dumbfounded when Maid Marian pecked him on the cheek in gratitude for saving her. (DW: Robot of Sherwood)
Though he initially stated that murder was against his moral code, it remains unknown if he killed the Half-Face Man himself, or if the android jumped to his death. Indeed, the Doctor showed some reluctance killing the Half-Face Man, offering him a drink of alcohol and trying to persuade the clockwork droid to self-destruct of his own free will. (DW: Deep Breath)
Much like his seventh and war incarnations, the Twelfth Doctor was heavily inclined to err toward a greater good and was willing to allow one inevitable death if it meant saving the majority. Through this attitude, he acted like a pragmatist that would not hesitate to abandon someone whose fate was already sealed. (DW: Into the Dalek)
Also like his previous incarnation, he relied on his companions to keep him from succumbing to his darker nature, but, unlike his predecessors, the Twelfth Doctor actively praised them for it, even claiming that Clara Oswald needed a "pay raise" for dealing with him. (DW: Into the Dalek)
Following his long stalemate with the Daleks on Trenzalore, this Doctor's hatred toward the Dalek species was rigid, with Clara describing it as "prejudice." He seemed conditioned to believe Daleks could not change and was closed-minded as he dealt with their presence. After his act of fixing a malfunctioning "good" Dalek caused it to revert to evil, the Doctor was almost pleased that his belief of there being "no such thing as a good Dalek" was vindicated. This horrified Clara, who became angered to the point of slapping him. (DW: Into the Dalek)
Habits and Quirks
When proposing a theory, the Doctor would use words such as "question" or "proposition", and would begin his conclusion with "answer" or "conjecture". After working out the important questions in his head, he waited for others to come to the same conclusion, becoming increasingly annoyed with each wrong question they proposed. (DW: Deep Breath)
Much like his predecessor, the Twelfth Doctor also used hand gestures to extenuate a point, but applied more dedication to his movements, standing firm, while speaking with conviction, (DW: Deep Breath) though would become more spontaneous when thinking intensely. (DW: Time Heist)
Highly observant, the Doctor was able to point out the Half-Face Man as non-human from his lack of interest in a burnt dinosaur corpse, and later noticed that he and Clara were trapped in a room full of Clockwork Droids due to only them breathing. (DW: Deep Breath) He was also able to make accurate deductions from observing his surroundings, identifying the Aristotle as a medical ship within seconds of being onboard. (DW: Into the Dalek)
Strong and durable, the Doctor was able to support his own weight singlehanded and shook off a fall down a tree with relative ease, though the latter can be linked to him still being within the early hours of his regeneration. (DW: Deep Breath)
Like several of his predecessors, the Twelfth Doctor was both a highly proficient swordsman (DW: Robot of Sherwood) and showed skill in Venusian aikido, using it to defend himself from Abesse (NSA: The Blood Cell) and disarming a distracted Robin Hood. (DW: Robot of Sherwood)
Despite initially forgetting how to pilot his TARDIS due to post-regenerative trauma, (DW: The Time of the Doctor) the Doctor eventfully mastered his way around the TARDIS console, being able to save Journey Blue by piloting the TARDIS around her, one second before her ship exploded. (DW: Into the Dalek)
Like his second, tenth and eleventh incarnations, the Twelfth Doctor also displayed telepathic abilities, being able to link his mind with Rusty to show the Dalek the beauty of the universe, (DW: Into the Dalek) and put Rupert Pink to sleep by placing his index finger on his forehead, editing his memories while he did so. (DW: Listen)
The Twelfth Doctor's appearance differed greatly from his predecessor’s. While his previous incarnation had begun his life looking young, (DW: The End of Time) the Twelfth Doctor now appeared much older. He had short grey hair, a hooked nose and sharp silverly blue eyes, with big ears. (DW: The Time of the Doctor) He was of a light build. (DWA: Chime Time)
Most changed were his eyebrows, which went from "delicate" (DW: The Time of the Doctor) to extremely thick and furrowed. (DW: The Day of the Doctor) Startled by the change, the Doctor described them as "attack eyebrows" which could "take bottle tops off". (DW: Deep Breath)
The Twelfth Doctor initially wore his predecessor's clothes following his regeneration, (DW: The Time of the Doctor) but, due to his mental instability, Clara and the Paternoster Gang put him in a nightgown and slippers for bed rest. Wearing this, he escaped into London and found himself cold and dirtied from scavenging around in a rubbish-filled alley. He bought a coat with a set of fraying fingerless knit gloves from a tramp, exchanging his predecessor's watch for it. Shortly thereafter, he disguised himself as a Clockwork Droid, donning a black Victorian suit with a tie.
After having a chance to return to the TARDIS, though, the Doctor chose a new outfit for himself. He donned a navy blue cardigan with a white collared shirt, matching blue trousers that covered his ankles, and black brogue boots. Over the top, he sported a thigh-length, dark blue jacket with red lining, often wearing it with the top button done. On his left hand ring finger, he had a pair of gold rings, a normal gold band and a second ring with an emerald gemstone that rested atop the first band. (DW: Deep Breath)