Refers to the main performer in a film, play, or show. Often used in credits or promotional materials.
She was chosen as the star of that movie.
The leading actor's name is written in large letters on the poster.
主役 is a more general term for the leading role or protagonist, not necessarily limited to acting (e.g., in a story or event). 主演者 is specifically the leading actor in a performance.
Compound of 主演 (starring, leading role) and 者 (person).