If he’s really worse than Shakespeare’s Richard III, or Iago, your villain’s got problems–which will be passed on to both the writer and the reader.
Well, okay, how many of us have to worry whether the villains we make up are credible? Oh, but many people do like to try their hand had writing a story, so these tips may not come amiss. And fiction can sometimes help us to understand what we see and hear in real life.
My villains all have something in common–they justify themselves to themselves. The elasticity of this approach is limitless. Even Stalin, Mao, or Hitler could have used it, and very likely did.
P.S.–I don’t believe Richard was anywhere near the villain Shakespeare made him out to be. He’s a great example of what happens when your enemies win and get to write the history.