One who takes the leading part in a drama; hence, one who takes lead in some great scene, enterprise, conflict, or the like.
The writer must be a participant in the scene... like a film director who writes his own scripts, does his own camera work, and somehow manages to film himself in action, as the protagonist or at least the main character. Hunter S. Thompson
Think 'Game of Thrones.' In the old days, this sort of show might be considered bad writing. It doesn't really seem to be moving toward a crisis or climax, it has no true protagonist, and it's structured less like a TV show or a movie than a soap opera. Douglas Rushkoff
The main question in drama, the way I was taught, is always, 'What does the protagonist want?' That's what drama is. It comes down to that. It's not about theme, it's not about ideas, it's not about setting, but what the protagonist wants. David Mamet