system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do actors alter their credited name slightly between films, often long after they are an established name?
gpt
If an actor wants to join an actor's union (which is basically a requirement if they want to work in Hollywood) they can't use the same name as someone who is already in the union. 

Sometimes actors will use a different name on a film in order to avoid certain union rules governing their participation in those films including minimum pay and other union required accommodations.