Dolores Umbridge (Imelda Staunton), wearing pink and with a fat face and a smug smile. fantasy, grimdark

Most people consider Dolores Umbridge to be one of the most evil characters in the Harry Potter universe. Even though Sirius Black says that the world isn't made up of just good people and Death Eaters, Dolores Umbridge (spoiler alert) DOES end up serving in Voldemort's dark regime when the Ministry of Magic falls in Book 7. She is a rigid, narrow-minded, hateful bureaucrat who loves her own power. In her way, she is more frightening than Voldemort because there are so many people like her in real life, and they ruin lives.

Imelda Staunton, the actress who played Umbridge in the movies, is a brilliant performer. She inhabited one of the most despised characters in the Potterverse and made her frighteningly real. She is good in so many things she does.