What is Oliver's last name?

Please, answer the desperate call of an obsessed fangirl.

Oliver has been my favorite character from square one; more so once he went all bad-ass at the end of Glass Houses. Since then, I've been poring over the books until one day, I realized...I had no idea what his last name was. So, I was wondering if they might have mentioned it once in the book and I just missed it, or maybe it hasn't been said at all. So, if anybody could help me...fwa!