The Protagonist or main character is the central figure of a story. It is not necessarily clear what being this central figure exactly entails. The terms protagonist, main character and hero are variously (and rarely well) defined and depending on the source may denote different concepts. The word "protagonist" derives from the Greek πρωταγωνιστής (protagonistes), "one who plays the first part, chief actor.
The term protagonist is defined to be either always synonymous with the term main character, or it is defined as a different concept, in which case a single character still may (and usually will) serve the function of both the protagonist and main character, or the functions may be split.
In classical and later theater the protagonist is the character undergoing a dramatic change (peripeteia), both of his own character and external circumstances, with the plot either going from order to chaos, as in a tragedy, with a reversal of fortune bringing about the downfall of the protagonist, usually an exceptional individual, as a result of a tragic flaw (hamartia) in his personality; or from chaos to order, as in a comedy, with the protagonist going from misfortune to prosperity and from obscurity to prominence.
A story about an exceptional character being a driving force behind the plot, facing an opponent (the antagonist) and undergoing an important change like it is the case with the protagonist may be told from the perspective of a different character (who may, but will not necessarily also be the narrator). In such cases it may be helpful to define the character through whose perspective the plot is followed as the main character, the main character having here a separate function from the protagonist.
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. (Note that the term antagonist in this context is much more recent than the term protagonist, and rests on the same misconception as the use of protagonist to mean proponent. See below.)
Sometimes, a work will initially highlight a particular character, as though they were the protagonist, and then unexpectedly dispose of that character as a dramatic device. Such a character is called a false protagonist.
When the work contains subplots, these may have different protagonists from the main plot. In some novels, protagonist may be impossible to pick out, because the plots do not permit clear identification of one as the main plot, as in Alexander Solzhenitsyn's The First Circle, depicting a variety of characters imprisoned and living in a gulag camp.
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, taking supplementary roles as auxiliary egos.