In order to be a truly evil character, one must possess a consciousness of no remorse. Evil characters, whether in books or movies, have no type of guilt nor sorrow for what they do to others. They are not afraid to embrace their darker side and to use to achieve their means/satisfaction.
They also have a disdain for what the majority society consider to be proper, right, and/or correct. In other words, they do not give bullocks for what others think of them. They believe that just proprieties for the more compliant and good among the population.
They really do not care about the consequences therein for their misdeeds. They let it RIDE to the ultimate conclusion. They are in it for the thrills. They are the BOSS of their lives and the lives they decide to dominate. They do not believe in abiding the rules that most people abide by. They invert society's rules to their ultimate benefit.
They want people to hate and loathe them. They really are concerned with being well-liked and popular. In fact, they loathe such. They thrive on being unpopular. They are the anti-popular. They glorify in being anti-popular and wear that badge with honor and demonic relish.
They exude a dark aura. They have a sinister quality which people are drawn to and repulsed by simultaneously. They revel in this sinister darkness. They also have the power, if in a powerful or an authoritative position, to have others do their biding while they sit back and watch the havoc and bedlam created.
Evil characters are excellent manipulators. To them, manipulating others is par for the course. They view others as pawns to do with as they will. They do not feel bad about this whatsoever. They believe that if others let themselves be manipulated, then it is their weakness, stupidity, or naivete which permit them to be so.
They ENJOY and RELISH being evil. Being evil is as natural to them as living and breathing is to most people. Evil to them is a friend, companion, muse, and lover. Being evil is their lifeblood and reason to exist. It gives them a reason to BE......and to THRIVE...... My favorite evil character is Mrs. Newless a/k/a Elizabeth Selwyn in the horror classic, HORROR HOTEL a/k/a CITY OF THE DEAD.