You've probably heard that no story is completely original, that everything is copied from somewhere, and nothing anyone ever thinks or says is really unique. It's an awfully pessimistic way of looking at the creative endeavor, but there's a degree of truth in it.
Any time you make up a new character, you are sure to be inspired by something you observed somewhere else. Perhaps you wondered, "What if there were a dwarven rogue, whose personality was a mix between Sherlock Holmes and Jack Sparrow?" or "My undead warrior is a lot like Frankenstein's monster, not evil so much as tragically neglected and rejected. He also likes to play with dolls." All this is fine and good for roleplaying, as long as you recognize the essential differences between your character and his or her inspirational anscestors.
After all, every creative endeavor basically consists of mix-and-matching pre-existing knowledge in new and useful ways. In the same way a painter doesn't need to invent new colors, color palettes, or even new color matching techniques to make an beautiful, a storyteller doesn't need to create entirely new characteristics for each character in his or her story, only mix-and-match qualities real people already have in order to create someone compelling and interesting for other characters to interact with.
Jump on in to find some great inspirations for WoW characters.