Who is Antagonist from Characters and Viewpoint and what is their importance?

The antagonist is the other main type of character defined by the author. This is the character who, according to the author, provides the opposition to the protagonist—physical, emotional, or spiritual. The antagonist, as the result of that opposition, triggers (consciously or unconsciously) the process of change undergone by the protagonist, and makes him/her strive harder to achieve that goal.