Assuming you have read (or at least seen the movie) Order of the Phoenix then you are familiar with Umbridge. So what makes Stephen King proclaim her so villainous (and what makes her possibly the most hated HP character)?
Well let’s look at her character in detail, this post, sums it up nicely she is lawful evil. She is the kind of evil we see in the world, . She is a bully someone who uses her position to do horrible things. She is someone who sees what she is doing (no matter horrible )as the right thing. She views herself as a loyal ministry employee stamping out corruption in society.
Chaotic evil like Voldemort or Bellatrix Lestrange are rare, but individuals who abuse our trust and bully others are something we see every day. That is what makes Umbridge such a horrifying villain, she is not abstract evil, she is very re.al and likely reminds of someone we have met (just far more heinous).
So this is all about writing your charaters so whtat does our picture of lawful evil have to do wit that? Think about your villains (even your plain old antagonists) are they purely evil villains are theiry more like Umbridge? What motivates them, why do they do what they do? Looke at Umbridge’s motivations and what made her got sch extreme lengths. Can your villain be put in a similar situation? Would they go to such lengths?