7. He's Clever
Perhaps more than any other Doctor, Ten emphasizes his cleverness at every available opportunity. You know a situation is going to get a serious out-smarting when Ten pulls out his glasses and crinkles his nose. Ten's cleverness is essential, because it is both his making and his undoing. His intelligence makes him charming and fun, knowing he can tackle any problem or situation he encounters, while simultaneously giving him the boldness to make grave mistakes, such as trying to re-write the future in "The Waters of Mars." Ultimately, though, it is his cleverness that leads him to recognize his arrogance, and thus sacrifice himself for Wilf one of the most touching moments in the entire Who canon.