He's not deep or complex compared to other characters in other series, or god forbid, other types of media, but at least he's not horribly cliche. I would argue that it's not quite clear what drives him. He likes to fight, but a lot of the time it's quite conveniently the morally correct course of action. He did kill the old captain to become the new captain, but in all the fights we see, he doesn't kill them if they're too weak or they walk away. He wants to know his sword's name as he understands the pain of not having one himself, but he can hear his sword, maybe because he's not a people person, or maybe because he's just too arrogant.