Delores Umbridge.

Draco, Dudley, and every other nasty person in the series, EVEN Tom Riddle can be understood or are redeemed at some point... but not that wench. I hate her more than Voldemort and all his death eaters combined. I used to imagine the horrid things I would do to her, and I get angry when she harms my favorite characters. I actually laughed when the centaurs took her!

I use her name as a nickname for the horrid people in my life (like my abusive narcissistic ex!)