The main character in a literary work.
Example:
Macbeth is the ruthlessly ambitious protagonist of Shakespeare's play, but it is his wife who pulls the strings.
Struggle, or conflict, is central to drama. The protagonist or hero of a play is involved in a struggle, either against someone or something else or even against his or her own emotions. So the hero is the "first struggler," which is the literal meaning of the Greek word protagonistes. A character who opposes the hero is the antagonist, from a Greek verb that means literally "to struggle against."