If the Player Characters represent a heroic and positive force in the world, Villains are the opposite. Being the Game Master, it is your responsibility to create, introduce, and portray these characters.
You already know about what differentiates a Villain from a typical Non-Player Character in terms of rules: that is to say, the access to Ultima Points. This section, on the other hand, contains advice on what you should focus on when creating and portraying an antagonist within the story.
So, let’s get to it: what makes a good Villain?
This is the most important aspect of any antagonist: they want to accomplish something. Be it reshaping the world, exacting revenge upon those who made them suffer, or conquering a neighboring region, Villains must have goals.
Goals are extremely useful for you as a Game Master: when you don’t know how a Villain would act or react to a given situation, look at their goals and you will most likely find an answer.
Remember that Villains can also escalate: perhaps a young wizard (minor Villain) suddenly realizes he must steal magical energy from an entire country to revive a loved one, thus becoming a major Villain. Then, when the attempt fails — likely due to the Player Characters’ intervention — the desperate wizard seeks a way to merge with the deities of time and space, erasing reality and creating a timeline that never was... a fitting and tragic goal for a supreme Villain.
Having some Villains turn into allies throughout the campaign is just as important: this encourages Players to seek dialogue with their adversaries and to consider both sides of a situation, instead of simply assuming that everyone is either good or evil.