Let’s talk a little about how to write your villain’s backstory. It’s simple enough, just answer these five questions:
What is your villain? Human? Alien? Monster? Is he a boy, or is she a girl [/Professor Oak]? What does he look like? What are his talents and his flaws? What does he want out of life? What does he like, what does he hate?
Where was your villain born? This is a far more complex question than a simple location. ‘When’ should be included here, as part of the where, for one thing. Circumstances around the birth need to be decided, too. Was your villain born in poverty or wealth? Where was he raised? Near where he was born? Also consider where your villain gained his education, any that he might have had (one can learn, even on the streets or trapped in a lab) and where did life take him between the beginning of his existence and where he shows up in the story? You could boil the questions down to where is your villain headed? and where is your villain from?
To whom was your villain born? Who raised him? Who taught him? Who is important to your villain? Who does he hate? Who does he know?
Go back to every question you already answered, break out your inner two-year-old, and ask ‘why’ to everything. Some things are less useful to ask ‘why’ to, of course. “Why is my villain human?” may not be particularly useful, especially if the only race in your whole story is human. The question may be more useful if you have other races, if instead the question is, “Why not use X other race?” but if, in the end, race is somewhat arbitrary, I suppose it won’t matter if he’s a Human or an Elf or an Asari (in which case I guess it’d be a woman).
However, some ‘why’s are very important: why is X important to him? Why does he want X out of life? Why was he raised in X place?
This question is also best treated as ‘why’ but perhaps a bit more judiciously. How does he use his talents/cope with his flaws? How does he accomplish X? If ‘where’ includes several different locations, how does he travel from one place to the other? How does he treat the ones that matter to him, how does he protect them?
After this, you should have a fairly well fleshed-out backstory. You should look over it, stretch it out, polish it up. Never be afraid to radically change pieces or the whole thing as your story develops. But always know your villain’s backstory – it will help determine his motive.