As a person
1. Think about your character's upbringing. Where and when was it, what was it like, and what of the family members and their relationships with your character?
2. Think about your character's aspirations. What formed them (or the lack of them), and are they close to achieving them, or are they still trying?
3. Are there any major events that still affect your character today? Did he get into a great University? Have to drop out of high school? Maybe their dream-job fell in his lap, or one little mistake they made ruined the rest of his future.
4. Are there any people, or groups of people, in your character's life, that changed or affected them, or simply were important to them?
5. What does your character do for a living?
6. What's your character's paper trail look like? (Does he have a criminal record, fame, a list of achievments, a lofty education, or a strange lack of documented information, for instance?)
7. How did your character come about being more/less than human? Does he have a mentor to this end, and what is his relationship with them?
8. How does this status affect his day to day life, or his life in the long term?