The Doctor's backstory has been discussed in length, both the original and the later revelation that most of it was a lie, that he/she was actually from another world, used as a genetic template to create the first Time Lords.

Dooku is one of my top favorite Star Wars characters. He used the darkside without being overwhelmed by it and his elegant fencing-like dueling style (Makashi) encouraged me to learn it.

He's not a poltergeist. Movies keep getting poltergeists all wrong. Poltergeists are not ghosts or spirits. They are surges of psychic energy. They have no consciousness or will. They are the product of psychic trauma normally formed by violent supernatural occurrences or a psychic under a great deal of emotional stress.