Antagonist

The protagonist of a plot is essentially the "bad guy". They aim to stop the protagonist from reaching his goals or to simply contradict him.

Examples
In Lord of the Flies, Jack is considered the antagonist because he is an opposite to the protagonist, Ralph.

“I ought to be chief,” said Jack with simple arrogance, “because I’m chapter chorister and head boy. I can sing C sharp.”

Synonyms

 * bad guy


 * enemy