The characters in a film are what moves the narrative forward. It’s the characters’ desires and traits that provide the motivations for a story to progress in a ‘natural’ way.
Main characters are usually established early on in the film when their motivations, traits and characteristics are revealed. Often, motivations come down to one of two things, money or love.
Usually in a film the main character will change in some way. They will learn something about themselves along the way. They may learn they were stronger than they thought or that money doesn’t mean everything.