Next to Sirius, he is one of my favorite characters, and also one of the more complicated characters in the series.
I imagine we'll find out what his deal is one of these days. I understand why he hates Sirius, that's a given. But why is he so nasty to Harry while at the same time trying to protect him? It's strange.
Of course, I have faith in J.K. Rowling, and I trust that these questions will be answered. But in the meantime, what do you guys think?