Born to a wealthy, snobby, social-climbing banker, George Osborne lives in the lap of luxury. Because of his good looks and manners, he fancies himself the perfect gentleman. His hasty marriage to Amelia proves that he is actually a disloyal cad. He dies on the battlefield a few months after becoming a husband.
It's hard out there for George Osborne. Why is it so hard? Well, in Thackeray's world everyone is constantly jockeying for position, trying to get closer and closer to the top of the social heap. At the top of that heap are the nobility and aristocrats – people born with titles (though not necessarily money). The males of this highest species are called gentlemen, which tends to mean that they have both the blood and the superficial good breeding (manners, primarily) to thrive in polite society.
George Osborne was born with really good looks and raised to have the manners of the aristocracy. Sadly, though, he lacks actual noble blood, so the whole situation is crazily frustrating. All he wants is to be a gentleman, but all he can do is pass for one rather than actually be one. And pass for one he does, quite well (as Rawdon tells Miss Crawley, you'd never be able to tell the difference between him and someone of noble birth).
Absent the blue-blooded interior, George is hell-bent on ornamenting his exterior. If anything, he is even more concerned with his appearance than any of the women in the novel. He is constantly staring at himself in mirrors and adjusting his clothing. Even more amazing, when he sets out to buy Amelia a present, he ends up buying one for himself instead. What does he buy? Diamond jewelry.
On top of this self-decoration, George is really into a few other markers of being a gentleman. One is his dedication to upholding his honor, which is hard because when it comes down to it, he's not all that honorable. He does the seemingly honorable thing of marrying Amelia, but two months later he's ready to ditch her and run off with Becky. The same thing happens with his idea of being an awesome soldier, displaying gentlemanly military prowess and valor as an officer. Here too, he can only get the outside of things right: his uniform looks terrific and he has a little boy's idea of what being a war hero is all about, but he is no more able to command his men than he is to distinguish himself in combat.
Fittingly, in the end, George dies face-down in a pile of mud, which is a nicely ironic comeuppance for a fellow so in love with his own face. Amelia is left to love and worship his portrait. The question we have to ask ourselves is, was he ever anything more than the portrait to begin with?