Villains

So i have a question about villains and how they're written in general. I've always been interested in villains and what happens 'after' the fact. After their punishment (assuming it's not fatal) and I try nto to write (in my RP's at least) 'throw away' villains who are just mindlessly evil. I like villains to have a grounded reason for their particular brand of wrong, as I feel it makes them more relateable and maybe even scarrier. It's easy to hate someone who is just evil for evil's sake but a person where you can see the logic as to why they do somethign seems a lot more of a character to me and feels like they are more of the world instead of just being a monster for the hero to defeat.

So my question is, does anyone have any advice or feedback they can give me on villains and how to write a villain that isn't just a paper cut-out? Villains like Kerrigan or Sylvannas (for those of you who know them) or even Harley Quinn. Sympathetic and you can see why they became the way they were.

Also seeing as I'm writing (or trying to write) a story that deals with the idea of villainy, i need the feedback.

On a side note i can't see any of my forum threads. Somebody suggested deleting my cache, which I did (twice) but I still can't see them. Any suggestions? >.>