The best villains have a stated goal
What separates the memorable antagonists from the forgettable ones is usually that their plan is coherent and explicable in a sentence. They want to rebalance something, control something, conceal something, or take a place they believe is rightfully theirs.
Several questions ask about motive rather than identity, and motive is often the easier route in. If you can remember what a character wanted, you can usually recover who they were.