"Character is that which reveals moral purpose, showing what kind of things a man chooses or avoids" -- Aristotle, from The Poetics
The persona: a series of masks which someone hides behind to create who they truly are-- a person. Seems contradictory, doesn't it? The individual is not easy to comprehend; they sometimes wear different masks because society forces them to play different roles, some more than others. Although it seems like a terrible thing, it isn't at all; for if we don't wear masks, it would be impossibly to function socially. To "unmask" Balthier would be a difficult process; however, I suppose we could break it down somehow.
The most prominent characteristic about Balthier is one that consensus gentium tells us: a charming and dashing man complete with his own sense of wit. Albeit, it's something more of a facade to cover up the emotional scars of his past. But even saying that would be taking it too far. He is, undoubtedly, a funny character who contributes brining to life a story about war. He's somewhat cynical to a fault; at first, we learn that he could be rather untrusting of others no matter how innocent they may seem, especially to Larsa. However, Balthier is a sharp character, and trusts his own intuition when relying on others. As the story progresses, he learns to warm up to the other party members, even up to the point where he sides with the resistance and its cause, despite all his efforts to avoid involvement with the ongoing war conflict.
Although pirates are generally noted for their notorious behavior, as shown by Ba'Gamnan and his posse, Balthier is a genuinely noble character. He does what he can to help the princess' cause, but not without some kind of price. Even so, he never asks for a heavy payment-- that is, if he ever receives one at all. He constantly faces the question of honor, with Basch as his foil. Honor, to him, means nothing if one cannot stand up for himself if they know something is wrong. He left Archadia with its ridiculous, chivalrous ideals and philosophy for a damn good reason. Perhaps he does retain some of that pride and self-confidence, especially when it comes to his handling of Airships and his certainty of being the Leading Man.
He's somewhat self-conscious about his vanity; some of his most memorable quotes would be remarks about his hygiene. Like most of the young male characters in the game who keep up some kind of effeminate status, Balthier certainly likes to keep clean. He would complain about "soiling his cuffs" while in the Rabanastre sewers, or even boldly requesting a bath from his highness of Bhujerba. Because of his seemingly joking character, it's up for debate if we should take him seriously or not (I'm myself am for the latter). That isn't to say he's self-centered and vain to a fault; it's clearly evident that his almost fateful sacrifice at the end of the game proves that, if anything, he's rather selfless.