Shylock becomes the true villain when he atkes Antonio to court. These actions prove that Antonio is mistreated by Shylock, the villain. He mistreats too many people, and then asks for mercy in a court. Shylock is mad for revenge towards all Christians, especially Antonio. He is such a villain that even his daughter and servant are eager to escape him.
Villains are oftenly antagonists in story plots and normally are a threat to the main character.
Villains normally have motives behind their evil doings.