As a character, the Ninth Doctor is less of a central heroic figure than an enabler, encouraging his companions and other people he meets to act upon their more positive impulses. Those he meets (in particular Captain Jack Harkness) often credit him with making them better people (this is indirectly referenced in the penultimate episode of Series 3 when the Master calls the Doctor "the man who makes people better"). He uses this quality alongside his intelligence and the information he gathers to inspire and allow others to act to end the dangers they face, rarely taking direct action himself (although he tended to find himself incapacitated in some manner at crucial moments, therefore requiring the interventions of others).
The Doctor's ninth incarnation was perhaps the most gritty, working class and informal, masking a lonely, guilt-ridden and melancholic personality with a jovial, witty, forthright and almost manic exterior. Similar to the Fourth Doctor, he would often make jokes in the face of danger, but then become grim and serious when on his own. Like the Sixth Doctor, he also tended to be fatalistic at times, to the point of near-panic when he and Rose were cornered in "The Unquiet Dead" and he realised that he was going to die (this despite the knowledge that he would probably just regenerate). Despite being impatient with humans, whom he often referred to as "stupid apes" -- and Mickey receiving particular scorn and being dubbed "Mickey the Idiot" -- the Ninth Doctor was far more tactile with, and reliant upon, his human companions than previous incarnations. He was notably both sentimental and emotional, especially where his closest friend, Rose, was concerned, to the point of allowing her to view her parents' wedding and later, her father's last moments — this being just one example of his occasional lack of caution.
The Ninth Doctor was quite colloquial in his language and spoke with a distinctly Northern accent. Although the Seventh and Eighth Doctor spoke with non-Received Pronunciation accents, the Ninth's era was the first time this was commented on in the series. When Rose questioned him on why, if he was alien, he sounded like he was from the North, the Doctor retorted, "Lots of planets have a North!"
Much of the Ninth Doctor's melancholy, lack of patience, levels of inaction and hard-bitten edge could be attributed to feelings of guilt at being the sole survivor of the Last Great Time War between the Time Lords and the Daleks, the conclusion of which apparently resulted from his own actions to end the Dalek threat, burning away 10 million of their ships and destroying Gallifrey and his own race in the process. This darker side came to the fore when he encountered the lone Dalek in "Dalek", exhibiting an angry, merciless and vengeful streak which surprised even Rose and led to the Dalek commenting that the Doctor would make a good Dalek. Previously, echoing the ruthlessness of his seventh self, he also impassively stood by as the villainous Lady Cassandra exploded, viewing it a fitting end for her actions (it was left ambiguous as to whether he could have spared her). However, a more light-hearted enthusiasm would surface on occasion, sometimes finding manic delight in tense situations such as his meeting with Charles Dickens (of whom he is a well-versed fan) whilst pursuing a kidnapped Rose. He also displayed a wide pop-cultural knowledge ranging from Dickens to 21st century celebrity gossip, while his joy on saving the victims of the nanogene attack in 1940s London, thus totally avoiding fatalities, restored some of his optimism and self-belief. Ultimately, the Doctor was able to put some of his demons to rest and seemed to find some peace through redemption towards the end of his incarnation. This redemption occurred shortly before his regeneration when he was given the opportunity to vanquish the Dalek fleet once more, this time at the cost of the human race, and decided not to do it. When the Dalek Emperor asks if he would rather be a coward or killer, the Doctor merely responds, "Coward. Any day."
In contrast with his successor and in common with his third, fourth and sixth selves, the Ninth Doctor did not shy away from using force in situations he would deem necessary. In "Dalek", he located an alien weapon for use on the last Dalek in existence; were it not for Rose's intervention, he would have used it. In "Bad Wolf", he and his companions escaped from the custody of the Gamestation's armed guards using physical force, with the Doctor throwing a guard against a wall. Later, as he proceeded to the station's control room, he wielded a heavy two-handed weapon, even deactivating the safety as if he was going to use it. However, as he speaks to the controller, he reveals that he had no actual intention of shooting anybody. The Doctor also arranged for lethal weaponry to be used on the Slitheen in "World War Three", sending a missile to destroy the alien family before they could nuke the world.
On several occasions, the Doctor indicates that he is 900 years old, the same age as the Sixth Doctor claimed to be in Revelation of the Daleks. This appears to contradict the original series in which the Seventh Doctor, following his regeneration in Time and the Rani, claimed to be 953 years of age, and who was in turn followed by the Eighth Doctor. To date this discrepancy has yet to be addressed on-screen. (See The Doctor's age.)
The Ninth Doctor's catchphrase, used in a variety of manners, and sometimes ironically, was "Fantastic!"
As befitting his more rugged, moodier behaviour, the Ninth Doctor was more streetwise in his appearance than his former selves. In deliberate contrast to the more notable and occasionally eccentric costumes of previous Doctors, the Ninth Doctor dressed in a non-descript, informal fashion: a worn, plain black leather jacket with a dark jumper (the only item he regularly changed, although only the colour, not the cut), trousers and boots. Charles Dickens, on learning the Doctor's name, declared that he more closely resembled a "navvy". Similarly, Jack Harkness, upon first meeting the Doctor and Rose, commented that they were definitely not dressed to blend into 1941 London, describing the Doctor's look as "U-boat captain." (The jacket was based on German Submariners jacket like the one used in Das Boot) Also, unlike other Doctors, he wore his hair close cropped.
The Ninth Doctor's era saw the introduction of a redesigned sonic screwdriver which was more versatile than its earlier versions, with functions ranging from its usual door opening abilities to conducting medical scans, repairing barbed wire and acting as a remote control for the TARDIS. The TARDIS console room also underwent a radical redesign, with an amber and green motif and a more organic look to its components.
The Ninth Doctor was also in the habit of using "slightly" psychic paper — that appeared to be a blank piece of card that had the ability to show the viewer anything that the user wanted them to see. The Doctor used this to fake various means of identification. Jack Harkness also used psychic paper in his capacity as a con man.
The Ninth Doctor modified Rose's mobile phone — which she dubbed the "superphone" — to give it the ability not just to receive and transmit where ordinary signals would not get through, but powerful enough to be able to make telephone calls to any point in time (even calibrating to the time period of the user).
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