Which best describes an antagonist? the main character, often a hero a well-developed character who is important to the story the character who is in conflict with the protagonist, a "bad guy" a poorly developed character

You got protagonist and antagonist mixed up. The antagonist is a person, group of people, or a force that opposes or dislikes the main character. The protagonist is the leading character in the story and is usually good. So the antagonist would be the bad guy and the protagonist would be the hero of a story.