I was just thinking past all my unused idea's when I suddenly put together this one. I'm not sure if it should be GURPS or D&D style.
He is an duel sword wielding fighter named Trean who has split personality.
If you are thinking Doctor Jackal and Mr Hide then you are in for a surprise. One of his personalities is extrordinarily innocent, similar to Elan {pre dashing swordsman} except he is also relatively competent. He is a strong beiliever in a simple philosophy. Don't strategize. Just charge in and hope for the best. He has a secret which even he... is fully aware of, he just thinks its normal. He's a half demon with extreme physical strength {all half demons have either lots of magical power, but physical weakness, or vise-versa, and they all look relitively normal for their base race.}he was originally raised by his mother, {the demon} in hopes of raising him to be evil. It failed.

Demon Lady: Alright you see a village what do you do. A} Burn it down. B}Burn it down and torture the populace. C}Obliterate it from existance.

Trean: I choose A, but only once the villagers are safely away of course. I then arrange to have better houses built, and everyone will be HAPPY!

Demon Lady: ....I think your missing the point.

This eventually frustrated her enough to make her attempt to change his personality through magic. She had put a lot of time into training him in combat after all. It ended up giving him his other side, the sarcastic jerk side. He every so often switches, from a nice innocent fighter, to a complete bastard, though not actaully evil, this side is far wittier than Trean. I heven't really worked out the details.
After this event she left him as a lost cause telling him to.
He is currently living in the same forest he grew up in.