A protagonist is the lead character, and in film, there can only be one. Your protagonist does not have to be likeable or even good, but they have to be your story’s focus. Dexter’s eponymous  role in the television series is a perfect example of this. He’s a heartless murderer, but the protagonist all the same.

One Character OnlyThis is because once you successfully manage to pull people into your story and out of their day-to-day lives they want to identify with one character only. Shakespeare’s Hamlet is a complicated character enough as it is.. Once the audience becomes comfortable with him, they don’t want to spend more time and effort trying to figure out his mother and step father, as well. It’s just too much work.

From a financial point of view, having more than one famous lead actor in a movie is costly. In 2006 Nicole Kidman was paid $17 million for The Invasion. Up until that year, Julia Roberts was paid $20 million per movie. It would hardly make sense to have those two women starring in the same film, therefore, because there’d hardly be any money left for anything else.

When movies have two main characters played by famous actors (such as Speed which Bullock shared with Keanu Reeves), one will always play the dominant role while the other will play a supportive one. In Speed, Reeves played the lead role. Besides this, there will usually be some commercial arrangement done with the lead actors involved.

That one will be the central character applies even to romances and buddy films like Lethal Weapon, starring Mel Gibson and Danny Glover. In the latter, it is Riggs (Gibson’s character) who plays the central role.

It is important to therefore identify who will play the lead character around which the entire story will revolve.