A villain is someone who deliberately harms other people or breaks the law in order to get what he or she wants.
N-COUNT
（小说、电影或戏剧中的）主要反面人物，反派主角
The villain in a novel, film, or play is the main bad character.
PHRASE
元凶;祸首;为害的人
If you say that someone is the villain of the piece, you are saying in a slightly humorous way that they are seen by some people as the cause of all the trouble in a particular situation.