A character who stands in the way of the protagonist is known as a/an _______.

http://contemporarylit.about.com/cs/literaryterms/g/antagonist.htm

an antagonist or "the villian".

A character who stands in the way of the protagonist is known as an antagonist. Antagonists are essential in storytelling as they create conflict and obstacles for the main character or protagonist to overcome. They can be individuals, groups, or even abstract concepts that oppose the goals or desires of the protagonist. Antagonists often serve as the main source of tension and conflict in a story. To discover this answer, you can use your understanding of storytelling elements or conduct a quick internet search related to characters in storytelling roles.