In some stories, a good villain is just as important as a good hero. Someone whose guts you can hate, who makes the hero's life as hard as it can possibly be, and whose demise you ultimately root for.
Everyone knows the villain of Harry Potter's story: the Dark Lord himself, Voldemort. And what a terrifying antagonist he is.
But I actually think there's a villain in the series that I hated even more than He-Who-Must-Not-Be-Named. That's right: I'm talking about the power-hungry, hair-bow-wearing, cat-plate-collecting UPPER MANAGEMENT NIGHTMARE, Ms. Dolores Umbridge.
Harry Potter and the Order of the Phoenix is one of my very favorites of the series. I actually love the risk J.K. Rowling took by making Harry a bit unlikeable. He's moody and irascible...but he's also 15 and saddled with a terrible burden. It makes absolute sense.
And then there's Dolores Umbridge. I hated her and her greedy, underhandedly unfair ways. I despised her cruel (and painful) punishments for Harry. When she succeeded Dumbledore as headmaster and her decrees got more and more ridiculous, I think I got physical hives. And I don't think I ever cheered as loudly during a book as when the fabulous Weasley twins gave her her comeuppance (thanks to a box of fireworks and their wicked sense of humor).
In her way, I think Umbridge is a scarier villain than Voldemort. Why? Because she seems so much more real. Voldemort is a dark wizard who is so evil, he doesn't even look human anymore. But Umbridge's flaw is ultimately a very human one: she seeks ambition and power above all else. And, unfortunately, I think we all see and hear of people, some in great power, whose failings are exactly that.