The great thing about HP fandom is that there are SO MANY minor characters or ones who are only named and then never seen again. So, even if you aren't all-knowing about the major characters, there are ones who are in need of personalities! The Lexicon (http://hp-lexicon.org/wizards/wizards_list.html) has a list of every character ever mentioned if you'd like to check that out for inspiration!

Sorry if that was annoying. ^^