I don't really know. I'm not very introspective. There are quite a few traits that I think define my personality though, and not just because I think they define me, but because they've been pointed out to me by other people.
Here's a list of them:
Dominant, aggressive, domineering, controlling, selfish, stubborn, self-absorbed, unreliable, rigid, resilient, confident, assertive, self-assured, secure, determined, egotistical, irresponsible, unemotional, optimistic, spontanious and pragmatic.