Other forms: tragic villains
A tragic villain is an evil character whose actions are at least partly explained by a very sad backstory. Darth Vader is a tragic villain, and so is Harry Potter's Severus Snape.
In books, plays, TV shows, and movies, the villain is the bad character who does mean or cruel things to other characters on purpose. This figure becomes more complicated and interesting when they have a tragic history, something overwhelmingly sad or traumatic that's led to their villainy. The monster in Frankenstein is a classic example of a tragic villain, turning to violence only after he's ostracized because of his fearsome appearance and becomes increasingly miserable and desperately lonely.