When designing a villain for an RPG, whether it be an NPC (non-player character) or a PC (player character), it is important to look at their goals and what they are seeking to do throughout the game's storyline. If you are designing a minor villain or a lower-tier one, their goals are probably going to seem fairly small and petty next to that of the game's penultimate BBEG (Big Bad Evil Guy/Girl/Person).
These minor or lower-tier villains may likely have very localized goals such as to take over a town or amass a horde of treasure and riches all for themselves. One possible tactic that they may employ in this quest for mediocrity, is to be mean to everyone as a way to scare them into submission. While you can definitely portray them this way, these kinds of villains run the risk of becoming boring in their usage of being mean just to be mean. Character whose only emotion is anger and hate are definitely viable characters, and they certainly have their place in many games, but they are typically seen more as thugs and brutes as opposed to criminal masterminds.
On the other hand, villains who utilize a variety of different emotions and tactics to woo their unsuspecting opponents into submission are, more often than not, seen as some of the best villains and BBEGs.
These characters may utilize tactics that include both local and global terror, world domination (no matter how benign), or the gathering of ultimate power. These are the kinds of villains who might, in some way, shape, or form, utilize the players' characters to accomplish their goals for them. These villains are sometimes referred to as "the one(s) you didn't see coming." To use pop-culture as the example, Freddy Kreuger (Nightmare on Elm Street) and Jason Voorhees (Friday the 13th) are villains, but of the thug and brute variety; whereas James Moriarty (Shelock Holmes stories) and Thanos (Marvel Comics) are villains of the "didn't seem them coming" variety.
No matter which version of villain you are designing to throw at your players (of which I exampled only two of the many varieties), creating a compelling backstory for them is essential to making them a believable threat to the world they inhabit. Without that all important backstory, your villain(s) might just turn into a random encounter, and I am pretty sure you probably want more for them than just that. So, as you are designing them, strive to give them well-thought-out backstories which will allow them to more fully take part in your game's world.
Test your imagination. Which is more terrifying:
The character of Thanos as played by Mickey Mouse (Walt Disney)? . . . OR
The character of Mickey Mouse as played by Thanos?