I liked the Ninth Doctor as being this "dark" Doctor... emotionally scarred from the Time War - fans commonly speculate that the Eighth Doctor was killed during the Time War, thus regenerating into the Ninth Doctor. The Tenth Doctor did say that the Meta-Doctor was like himself when he first met Rose as the Ninth Doctor; full of anger and emotional trauma from the Time War... and that Rose helped him to heal from that, and that she would do the same for the Meta-Doctor.