My favorite kind of monster is a tragic one.
We already know about the villain who doesn't see himself as evil. This character feels justified in his actions, whether from a skewed sense of right and wrong or because he's been wronged by others. There are many wonderful examples, including Valentine, President Snow, and Lord Voldemort. "There is no good and evil. There is only power and those too weak to seek it." - Voldemort
But one of my favorite characters is the almost villain. The one who believes he is evil and fights his nature, sometimes successfully and sometimes not. Typically, this is a paranormal being (vampire, werewolf, etc.) Often the character manifests as a "bad boy", but these traits certainly aren't necessary.
But why? Why am I such a sucker for the monster? Because if it's well written, I will root for the underdog. I will see his inner struggle and feel that much more horror when he gives in to it and that much more relief when he doesn't.
So who are some of these characters? Patch from Hush Hush might have been one of the best as I really didn't know until the very end whether he was "good" or "bad". But I can tell you that I was invested and hoping the good would win out. Other good examples? Cole from Linger, Ridley from Beautiful Creatures, and (yeah you knew I'd bring him in here somewhere) Damon.
Have you ever tried writing one of these sympathetic monsters? Was it difficult or easier than others? Who is your favorite? I'd love to know your thoughts.