The protagonist is there to kill, torture, terrorize and otherwise bring misery to the world.
Alternate names: Sadistic protagonist, Malicious protagonist, Evil protagonist, Villainous protagonist
The first video game about Malevolent protagonist was released in 1983.
Care should be taken when dealing with the revenge theme, as most cases usually are simply anti-heroic rather than malevolent in general (the malevolence is targeted at one or very few actual people). However, in some cases the point the protagonist vows vengeance they may also take a heel turn on moral issues (they no longer matter, for whatever the particular reason is in each case).