The Ninth Doctor
"If you are an alien, how comes you sound like you're from the North?"
"Lots of planets have a north."
- Rose Tyler and the Ninth Doctor talking about his accent in Rose
The Ninth Doctor's character is dominated by his reaction to the Last Great Time War, and to the loss of Gallifrey at the climax of that war. Whilst he retains the humour and flippancy of many of his former incarnations it is, to a certain extent, a mask covering his true sorrow and loneliness. When he lets the mask slip it may appear that he is suffering from rapid mood swings. Underneath the joviality and stupid grins the Doctor's character appears to be solid steel.
The war has made him harsher than many of his previous incarnations, he is, for example, willing to murder a reformed Dalek in cold blood. He looks down on the human race in a way that only his first incarnation had done before - frequently calling them "stupid apes". Whilst he is protective of those he has come to trust, such as Rose Tyler, he doesn't suffer fools gladly- being perhaps unfairly harsh on those who don't measure up to his standards.
His relationship with his companion Rose is perhaps one of the closer friendships the Doctor has had with one of his companions. The loss of Gallifrey means that he values his companion more than ever. Although this friendship has some of the outside trappings of human romances, such as holding hands (as, incidentally, the Third Doctor frequently did with his companion Jo), the ninth Doctor clearly does not have romantic feelings towards her, once telling her that "you look beautiful, considering." - referring to her being a human. It appears that the Doctor has finally discovered the human art of flirting and uses it to enhance his friendships.
The ninth Doctor's appearance is dominated by the battered leather jacket he wears, usually together with a jumper and some nondescript trousers and shoes. He has very short hair and reasonably large ears. He is notable for his northern accent.