Like some of those who replied before me (I actually read this time).
The villain need to be smart and have a bigger then average ego. That's about all it really need, other then being against the protagonist. If an antagonist isn't smart at all, or have normal person level of smartness, that character wouldn't make that much of a good villain. If they are just ruthless, it might make it feel like a simple grunt, regular level of smartness, he might feel more like a rival. A real villain need to plan ahead, conceive traps, multiple pointless steps for their plans, therefore always giving the protagonist an advantage, like speeches in the fight before they would otherwise win, and it need to be somewhat personal eventually. I like the smart rich, with white hairs on the side, small mustache and big whine glass in a mansion type of villain myself, or just type of character.