Following Through aka Why Voldemort is a Convincing Villain
"You will do my will." The generic villain sneered, a glint of wild malice in his coal black eyes. The hero laughed with an unparalleled confidence, "And why would I do that?" The villain cackles, "Because I..." The villains maniac grandeur faded, confusion clouding his once menacing eyes, "I'm, uh...not quite sure. I've threatened to kill many people, threatened to burn houses, and threatened to use your love of endangered parrots against you, but I haven't actually done anything of evil. All I've had are some evil intentions."
That has got to be the lamest villain ever. And sadly, I come across that way too much in novels these days. It's not that blatant usually (especially not the parrot thing), but the general gist stands. The villain makes a big deal of acting evil and cackling at any chance possible, but they haven't actually done anything worth mentioning in the Baddie World Records. Every good hero needs a good villain. And when villains look scary, sound scary, but don't actually do scary things, they aren't really villains after all.
That is why good ol' Voldy is such a good ol' villain.
He looks scary, sounds scary, and most important of all, acts scary. He kills without a moments hesitation, he has real motive, and he has a real heartless, unpredictable nature that makes you never know where he'll strike or how hard he'll strike. All you know is that it'll be bad, because he's Voldemort, and Voldemort is evil.
So, when you're writing the next Harry Potter, make sure your Voldy follows through with all the evil things he threatens to do.