A protagonist, meaning "one who plays the first part, chief actor") is the main character (the central or primary personal figure) of a literary, theatrical, cinematic, or musical narrative, who enters conflict because of the antagonist. The audience is intended to mostly identify with the protagonist. In the theatre of Ancient Greece, three actors played every main dramatic role in a tragedy; the protagonist played the leading role whereas the deuteragonist and the tritagonist played the others.

The terms protagonist and main character are variously explained and, depending on the source, may denote different concepts. In fiction, the story of the protagonist can be told from the perspective of a different character (who may also, but not necessarily, be the narrator). An example would be a narrator who relates the fate of several protagonists - perhaps as prominent figures recalled in a biographical perspective.

Sometimes, antagonists and protagonists may overlap, depending on what their ultimate objectives are considered to be. Often, the protagonist in a narrative is also the same person as the focal character, though the two terms are distinct. Excitement and intrigue alone is what the audience feels toward a focal character, while a sense of empathy about the character's objectives and emotions is what the audience feels toward the protagonist. Although the protagonist is often referred to as the "good guy", it is entirely possible for a story's protagonist to be the clear villain, or antihero, of the piece.

The principal opponent of the protagonist is a character known as the antagonist, who represents or creates obstacles that the protagonist must overcome. As with protagonists, there may be more than one antagonist in a story. The antagonist may be the story's hero; for example, where the protagonist is a criminal, the antagonist could be a law enforcement agent that tries to capture him.

Sometimes, a work will offer a particular character as the protagonist, only to dispose of that character unexpectedly, as a dramatic device. Such a character is called a false protagonist. Marion in Alfred Hitchcock's Psycho (1960) is a famous example.

When the work contains subplots, these may have different protagonists from the main plot. In some novels, the protagonists may be impossible to identify, because multiple plots in the novel do not permit clear identification of one as the main plot, such as in Alexander Solzhenitsyn's The First Circle, depicting a variety of characters imprisoned and living in a gulag camp, or in Leo Tolstoy's War and Peace, depicting 15 major characters involved in or affected by a war.

In psychodrama, the "protagonist" is the person (group member, patient or client) who decides to enact some significant aspect of his life, experiences or relationships on stage with the help of the psychodrama director and other group members; in this case, the protagonist takes supplementary roles as auxiliary egos.