The purpose of an antagonist in the story is to hinder the main character(s) from achieving their goal. The antagonist does not always have to be the main villain, but just has evil intentions to the main characters. A perfect example of this (in my opinion) would be Boba Fett from<em> The Empire Strikes Back</em>, he was not the main villain, but was hired by the main villain of the original trilogy to stop the main group from achieving their goals, and did have evil intentions towards them.
