Fan Casting Adaptation Personality Change in Sort by Tropes

Often when adapting from a book or other medium, a character will be included in the adaptation but their personality will be different from the original medium. Maybe they are a Composite Character and take on the role and personality of the one they get combined with. Maybe they only have a minor role initially but it gets expanded upon in the adaptation. Or maybe in the original their role was much bigger and got cut down in the adaptation, leaving them a little one dimensional.