The character who plays the central part of any work of literature is called a main character or a protagonist. This central part means that, while reading, we are mostly getting familiar with his actions, emotions, thoughts, and that his actions have the most impact on the development of the story or they act as a driving force to it. Most often the protagonist is a good guy, a hero in the story.
Contrary to the protagonist, there is an antagonist; complete opposition of the main character - opposite actions, motives, way of thinking.