He was a Phoenix, rising from the ashes of the war that killed his race and destroyed his planet. Ten million ships on fire and only he survived. As his TARDIS left Gallifrey for the last time, it made such a heart-breakingly beautiful sound that many people swore they heard the song of the phoenix. With his rebirth he changed.
He was a Dragon, majestic and deadly. The TARDIS flamed out and destroyed everyone. And wherever he went, disaster struck. So someone called him "Bringer of Death", even though Death brought him. He is the lonely dragon who lashes out until the fearless villager reaches out to him. He is the dragon who loved every one of his victims. He is the small vulnerable creature who wears protective armor to hide his feelings.
He is a Sphinx, who knows all but won't tell anything. He gives enough to perplex and lets you figure out the rest. He is the mystery no one can decipher. He can feel the earth turn. He can see everything - all that is; all that was; all that ever could be. He knows how it ended and how it will all begin - and he protects everyone from it.
He is the Doctor.